Transducer array imaging system

ABSTRACT

The disclosed embodiments include a method, system, and device for conducting ultrasound interrogation of a medium. The novel method includes transmitting a non-beamformed or beamformed ultrasound wave into the medium, receiving more than one echoed ultrasound wave from the medium, and converting the received echoed ultrasound wave into digital data. The novel method may further transmit the digital data. In some embodiments, the transmitting may be wireless. The novel device may include transducer elements, an analog-to-digital converter in communication with the transducer elements, and a transmitter in communication with the analog-to-digital converter. The transducers may operate to convert a first electrical energy into an ultrasound wave. The first electrical energy may or may not be beamformed. The transducers also may convert an echoed ultrasound wave into a second electrical energy. The analog-to-digital converter may convert the electrical energy into digital data, and the transmitter may transmit the digital data.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to U.S. patent application Ser. No. ______(Attorney Docket No. PENR-0003), U.S. patent application Ser. No. ______(Attorney Docket No. PENR-0010), U.S. patent application Ser. No. ______(Attorney Docket No. PENR-0011), U.S. patent application Ser. No. ______(Attorney Docket No. PENR-0012), U.S. patent application Ser. No. ______(Attorney Docket No. PENR-0013), U.S. patent application Ser. No. ______(Attorney Docket No. PENR-0014), U.S. patent application Ser. No. ______(Attorney Docket No. PENR-0016), U.S. patent application Ser. No. ______(Attorney Docket No. PENR-0017), U.S. patent application Ser. No. ______(Attorney Docket No. PENR-0018), U.S. patent application Ser. No. ______(Attorney Docket No. PENR-0019), U.S. patent application Ser. No. ______(Attorney Docket No. PENR-0020), U.S. patent application Ser. No. ______(Attorney Docket No. PENR-0021), U.S. patent application Ser. No. ______(Attorney Docket No. PENR-0022), U.S. patent application Ser. No. ______(Attorney Docket No. PENR-0023), U.S. patent application Ser. No. ______(Attorney Docket No. PENR-0024), U.S. patent application Ser. No. ______(Attorney Docket No. PENR-0025), all filed on Nov. 10, 2006, allentitled “Transducer Array Imaging System,” and all of which are hereinincorporated by reference in their entirety.

BACKGROUND

Many transducer-array based systems, such as ultrasound imaging systemsand including radar, sonar, optical, and audible sound systems and thelike, use a remote module sometimes referred to as a probe. The probetypically houses an array of transducers and the system typicallyperforms coherent signal processing. In the case of medical ultrasound,a user places the probe on the patient and the transducers emit energy(e.g., ultrasound waves) into the patient's body. The transducer arrayalso receives energy that is reflected or echoed by the patient's bodyback to the transducers. The received echo waves are converted toelectrical signals. The electrical signals are processed by the medicalimaging system in order to create a visual representation of thetargeted area inside the patient's body. Other non-medical uses ofultrasound include non-destructive testing of various materials.

Currently, medical imaging systems use typically large multi-conductorcables to carry the electrical signals from the probe to the system'smain processing unit. Because of the large number of transducer elementstypically required, a significant amount of energy is required to becarried by the cable. The relatively large cable creates difficultieselectrically, medically, and physically.

From a physical perspective, for example, the cable is ergonomicallyburdensome. From an electrical perspective, the larger cable degradesthe electrical interface to the main unit and adds capacitance to thesystem. By adding capacitance to the system, the impedance of the cableis significantly lower than the transducer array. As a result, thetransducers may need to be powered with greater currents. Also, thecable capacitance may undesirably result in a lower signal-to-noiseratio (SNR).

From a medical perspective, the cable creates a problem where sterilityis an issue. A probe used in a sterile field must either besterilizable, or must be covered with a sterile sheath. With a cabledprobe, the probe is covered with a sterile sheath that extends back overthe cable, yet the covered cable eventually extends out of the sterilefield because the main unit it not sterilizable. As the probe is used,the attached cable slides into and out of the sterile field. Once thecable slides out of the sterile field, the necessary sterility iscompromised. As a result, a user is limited in using and moving thecabled probe.

SUMMARY

The disclosed embodiments include a method, system, and device forconducting ultrasound interrogation of a medium. The novel methodincludes transmitting a non-beamformed or beamformed ultrasound waveinto the medium, receiving more than one echoed ultrasound wave from themedium, and converting the received echoed ultrasound wave into digitaldata. The novel method may further transmit the digital data. In someembodiments, the transmitting may be wireless. The novel device mayinclude transducer elements, an analog-to-digital converter incommunication with the transducer elements, and a transmitter incommunication with the analog-to-digital converter. The transducers mayoperate to convert a first electrical energy into an ultrasound wave.The first electrical energy may or may not be beamformed. Thetransducers also may convert an echoed ultrasound wave into a secondelectrical energy. The analog-to-digital converter may convert theelectrical energy into digital data, and the transmitter may transmitthe digital data.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating various components of an exampleprobe;

FIG. 2 is a block diagram illustrating various components of a mainunit;

FIG. 3 is a block diagram of a system for transmitting an acoustictransmit focused wave;

FIG. 4 is a block diagram of a system for receiving an acoustic transmitfocused wave;

FIGS. 5A-5C provide an example of different possible configurations andtechniques for providing interrogation of a medium;

FIG. 6 is a block diagram of a synthetic transmit focus ultrasoundsystem;

FIG. 7 is an example illustration of signals transmitted from each oftransducer elements and received back on respective transducer elements;

FIG. 8 illustrates just one example technique of decimating a number oftransducer elements that receive an echo ultrasound wave;

FIG. 9 is a flow diagram of a method for establishing a link between aprobe and a main unit;

FIG. 10 is a flow diagram of an inactivity timeout;

FIG. 11 is a block diagram of an example battery monitoring and controlcircuit;

FIG. 12 is a flow diagram of a power control technique;

FIG. 13 is a block diagram illustrating data merger and adaptivecontrol;

FIG. 14 is a block diagram of a circuit that provides locatorfunctionality;

FIG. 15 is a block diagram of a circuit that provides external sourcefunctionality, for example in a passive locator environment;

FIG. 16 is a graphical depiction of the signal levels, integration gain,gain control factor, and attenuated signal levels;

FIG. 17 is a graphical depiction of the number of bits of data requiredover a depth range of 0 to 80 mm for the parameters discussed withreference to FIG. 16;

FIG. 18 is a graphical depiction of a total amount of data required froma probe to a main unit with respect to depth of the acceptance angle andedge effects;

FIG. 19 is an illustration of an example image region of interest for alinear array transducer;

FIG. 20 is a block diagram employing a ping-pong frame buffer;

FIG. 21 is a timing diagram illustrating the acquisition of frames ofdata;

FIG. 22 is a timing diagram illustrating this frame adjustment; and

FIG. 23 is a chart representing a sequence of writes and reads to aping-pong frame buffer.

DETAILED DESCRIPTION

The subject matter of the described embodiments is described withspecificity to meet statutory requirements. However, the descriptionitself is not intended to limit the scope of this patent. Rather, theinventors have contemplated that the claimed subject matter might alsobe embodied in other ways, to include different steps or elementssimilar to the ones described in this document, in conjunction withother present or future technologies. Moreover, although the term “step”may be used herein to connote different aspects of methods employed, theterm should not be interpreted as implying any particular order among orbetween various steps herein disclosed unless and except when the orderof individual steps is explicitly described.

Similarly, with respect to the components shown in the Figures, itshould be appreciated that many other components may be included withthe scope of the embodiments. The components are selected to facilitateexplanation and understanding of the embodiments, and not to limit theembodiments to the components shown.

There are many transducer array systems contemplated by the disclosedembodiments. Most of the description focuses on a description of adiagnostic medical ultrasound system, however the disclosed embodimentsare not so limited. The description focuses on diagnostic medicalultrasound systems solely for the purposes of clarity and brevity. Itshould be appreciated that disclosed embodiments apply to numerous othertypes of methods and systems.

In a transducer array system, the transducer array is used to convert asignal from one format to another format. For example, with ultrasoundimaging the transducer converts an ultrasonic wave into an electricalsignal, while a RADAR system converts an electromagnetic wave into anelectrical signal. While the disclosed embodiments are described withreference to an ultrasound system, it should be appreciated that theembodiments contemplate application to many other systems. Such systemsinclude, without limitation, RADAR systems, optical systems, audiblesound reception systems. For example, in some embodiments, the audiblesound reception system may be used at a sporting event to detecton-field sounds with a large microphone and wirelessly transmit thesound back to a main unit.

In addition, although the disclosed embodiments are described withreference to a medical ultrasound system, it should be appreciated thatthe embodiments contemplate application to many other types ofultrasound system. For example, the disclosed embodiments apply tonon-destructive testing systems. Such non-destructive testing systemsmay be used to inspect metal, wood, plastics, etc. for structuralintegrity and/or to ascertain certain characteristics of the material.For example, the embodiments may be used to inspect piping for cracksand/or to determine their thickness. Also, non-destructive testingsystems may be used to inspect material connections, like metal welds,and the like.

Also, although the disclosed embodiments are described with reference toa diagnostic system, it should be appreciated that the embodimentscontemplate application to many other types of systems, including, forexample, therapeutic ultrasound systems.

FIG. 1 is a block diagram illustrating various components of an exampleprobe 100 according to one embodiment. It should be appreciated that anyor all of the components illustrated in FIG. 1 may be disposed within ahousing (not shown in FIG. 1) having any form factor. Probe 100 mayinclude circuitry that is represented in FIG. 1 as a series of blocks,each having a different function with respect to the operation of probe100. While the following discussion treats each of the blocks as aseparate entity, an embodiment contemplates that any or all of suchfunctions may be implemented by hardware and/or software that may becombined or divided into any number of components. For example, in oneembodiment the functions represented by any or all of the blocksillustrated in FIG. 1 may be performed by components of a single printedcircuit board or the like.

Transducer 102 represents any number of transducer elements that may bepresent in probe 100. Electroacoustic ultrasound transducer typesinclude piezoelectric, piezoceramic, capacitive, microfabricated,capacitive microfabricated, piezoelectric microfabricated, and the like.Some embodiments may include transducers for sonar, radar, optical,audible, or the like. Transducer 102 elements may be comprised ofindividual transmitter and receiver elements. For example, transmitter204 includes one or more transmitters that drive each of the transducerelements represented by transducer 102, as well as transmit and/orreceive switch circuitry that isolates transmitter 204 from a receiverchannel (which may be part of preamp 206 in FIG. 1) during the transmitevent. The transmitters may produce a focused, unfocused or defocusedtransmit beam, depending on the intended application. For example, thefocused beam may be useful when high peak acoustic pressure is desiredas is the case of harmonic imaging. One embodiment uses defocusedtransmit beams to provide insonfication or interrogation of a relativelylarger spatial region as required for synthetic transmit focusing. Thetransmit beam may be configured to elicit return echo information thatis sufficient to produce an ultrasound image along an imaging plane.

Probe 100 receiver circuitry (not shown in FIG. 1) may include alow-noise, high-gain preamplifier 206 for each receive channel (e.g.,manufactured by Texas Instruments model number VCA2615 dual-channelvariable gain amplifier or the like). Any number of receive channels maybe present in an embodiment. Preamplifier 206 may provide variable gainthroughout a data acquisition time interval. Preamplifier 206 may befollowed by bandpass filter 214 that may operate to reduce the noisebandwidth prior to analog-to-digital (A/D) conversion.

Transmit timing, time-gain control (TGC) and multiplexer control 212 mayin some embodiments provide timing and control of each transmitexcitation pulse, element multiplexer setting, and TGC waveform. Anexample unipolar transmitter channel circuit may include, for example, atransistor functioning as a high-voltage switch followed by a capacitor.The capacitor may be charged to a high voltage (e.g., 100V), and thendischarged through the transistor upon excitation by a trigger pulse.Similar transistor-based switches may also be used for transmit/receiveisolation, element-to-channel multiplexing, etc. Other embodiments mayinclude more sophisticated transmitters capable of bipolar excitationsand/or complex wave shaping and/or the like.

To focus the transmitted ultrasound energy at a desired spatiallocation, in some embodiments, the excitation pulse of each transducerelement may be delayed in time relative to the other elements. Such adelay pattern may cause the ultrasound waves from excited elements tocombine coherently at a particular point in space, for example. This maybe beneficial for a focused and/or an acoustic transmit focused system,for example. Alternatively, the transmit waveforms may be delayed insuch a way as to defocus the beam. This may be beneficial for a systememploying synthetic transmit focusing, for example.

In some embodiments, a TGC portion of block 212 may provide aprogrammable analog waveform to adjust the gain of variable gainpreamplifier 206. The analog waveform may be controlled by a userthrough a user interface such as, for example, a set of slide controlsused to create a piece-wise linear function. In some embodiments, thispiece-wise linear function may be calculated in software, and thenprogrammed into sequential addresses of a digital memory, for example.The digital memory may be read out sequentially at a known time intervalbeginning shortly after the transmit excitation pulse, for example. Insome embodiments, output of the memory may be fed into adigital-to-analog converter (DAC) to generate the analog waveform. Insome embodiments, time may be proportional to the depth of theultrasound echoes in the ultrasound receiver. As a result, echoesemanating from tissue deep within a patient's body may be attenuatedmore than those from shallow tissue and, therefore, require increasedgain. The controlling waveform may also be determined automatically bythe system by extracting gain information from the image data, forexample. Also, in some embodiments, the controlling waveform may bepredetermined and stored in the memory, and/or determined during systemoperation.

One embodiment may include a multiplexer within block 204 formultiplexing a relatively large array of transducer 102 elements into asmaller number of transmit and/or receive channels. Such multiplexingmay allow a smaller ultrasound aperture to slide across a full array onsuccessive transmit events. Both transmit and receive apertures may bereduced to the same number of channels or they may differ from eachother. For example, the full array may be used for transmitting while areduced aperture may be used on receive. It should be appreciated thatany combination of full and/or decimated arrays on both transmit andreceive are contemplated by the disclosed embodiments.

Multiplexing also may provide for building a synthetic receive apertureby acquiring different subsets of the full aperture on successivetransmit events. Multiplexing may also provide for the grouping ofelements by connecting adjacent elements on either transmit or receive.Grouping by different factors is also possible such as, for example,using a group of three elements on transmit and a group of two elementson receive. One embodiment may provide multiplexing for synthetictransmit focusing mode and multiplexing for acoustic transmit focusingmode and provide for switching from one mode to the other, for example,on frame boundaries. Other multiplexing schemes are also possible andare contemplated by the disclosed embodiments.

Multiplexing may be controlled by using transmit timing, TGC andmultiplexer control 212. Various transmit and/or receive elements may beselected when imaging a particular spatial region. For example,ultrasound echo data for an image frame may be acquired by sequentiallyinterrogating adjacent sub-regions of a patient's body until data forthe entire image frame has been acquired. In such a case, differentsub-apertures (which may include elements numbering less than the fullarray) may be used for some or all sub-regions. The multiplexer controlfunction may be programmed to select the appropriate sub-aperture(transmit and/or receive), for example, for each transmit excitation andeach image region. The multiplexer control function may also providecontrol of element grouping.

Analog to Digital (A/D) converter 218 may convert the analog image datareceived from probe 100 into digital data using any method. Digitaldemodulator 222 may include any type of digital complex mixer, low-passfilter and re-sampler after each AID converter channel, for example. Insome embodiments, the digital mixer may modulate the received image datato a frequency other than a center frequency of probe 100. It someembodiments, this function may be performed digitally rather than in theanalog or sampling domains to provide optimum flexibility and minimalanalog circuit complexity. The low-pass filter may reduce the signalbandwidth after mixing and before re-sampling when a lower sampling rateis desired. One embodiment may use quadrature sampling at A/D converter218 and, therefore, such an embodiment may not require a quadraturemixer to translate the digital data (e.g., radio frequency (RF)) signalsof transducer 102 to a baseband frequency. However, complex demodulationby means of an analog or digital mixer or the like may also be used inconnection with an embodiment.

Memory buffer 224 may have sufficient storage capacity to store up to,for example, two frames of data. Such a frame-sized buffer 224 may allowframes to be acquired at a rate substantially higher than the rate atwhich frames can be transferred to main unit 130 (or some other device)across wireless interface 120, for example. Such a configuration may, inan embodiment, be preferable to acquiring each frame over a longer timeinterval because a longer time interval may reduce a coherence of theacquired data throughout the frame. If frame transmission rates are atleast as fast as frame acquisition rates, a smaller memory buffer 224may be used in some embodiments. One embodiment uses a “ping-pong”buffer fed by the receiver channels as memory buffer 224. Data frommultiple channels may be time interleaved into memory buffer 224. Forexample, 32 receiver channels each sampled at the rate of 6 MHz wouldproduce a total baseband data rate of 192M words per second, which iswell within the rates of conventional DDR2 SDRAM. The ping-pong natureof memory buffer 224 may allow new data to fill buffer 224 whilepreviously acquired data is read from memory and sent to wirelessinterface 120, for example.

Memory buffer 224 is followed by data merger 226. Data merger 226 mayoperate to merge receive channel data into one or more data streamsbefore advancing the data stream to wireless interface 120 fortransmission to main unit 130, for example. Data from data merger 226may be sent across wireless interface 120 (and/or across wired interface122) at a rate that is appropriate for the transmission medium. The datafrom the receive channels may be multiplexed in some fashion prior totransmission over wireless interface 120 and/or wired interface 122. Forexample, time-division multiplexing (TDM) may be used. Other types ofmultiplexing are also possible such as, for example, frequency-divisionmultiplexing (FDM), code-division multiplexing (CDM), and/or somecombination of these or other multiplexing techniques.

In addition to image data transfer, control information may betransferred between probe 100 and main unit 130. Such control data maybe transferred over the same communication link, such as wirelessinterface 120 and/or wired interface 122, or some other communicationlink. Control commands may be communicated between main unit 130 andprobe 100 (and/or some other devices). Such control commands may servevarious purposes, including for example, instructing a mode of operationand/or various imaging parameters such as maximum imaging depth,sampling rate, element multiplexing configuration, etc. Also, controlcommands may be communicated between probe 100 and main unit 130 tocommunicate probe-based user controls 104 (e.g., button pushes) andprobe operational status (e.g., battery level from power supplymanagement 230), and the like.

The probe's status may include an indicator and/or display of certainvalues relevant to the operation of the system. For example, theindicator may be visible, audio, and/or some combination thereof.Without limitation, the indicator may indicate power status, designationof device, type of device, frequency range, array configuration, powerwarnings, capability of a remote unit, quality of transmission ofdigital data, quantity of errors in transmission of digital data,availability of power required for transmission of digital data, changein transmission rate, completion of transmission, quality of datatransmission, look-up tables, programming code for field programmablegate arrays and microcontrollers, transmission characteristics of thenon-beamformed ultrasound wave, processing characteristics of the echoedultrasound wave, processing characteristics of the digital data, and/ortransmission characteristics of the digital data, etc. Also, theindicator may show characteristics of a power source like capacity,type, charge state, power state, and age of power source.

In some embodiments, data/control arbiter 228 may be responsible formerging control information and image data communicated between probe100 and main unit 130. The control information may be passed fromcontrol interface 232, where it is collected to data/control arbiter 228for transmission to main unit 130. In some embodiments, control andimage data may be distinguishable from each other when sent acrosswireless interface 120 and/or wired interface 122 to facilitate properhandling at main unit 130. In other embodiments, there may be no suchdistinction. In addition, data/control arbiter 228 may accept controlcommands from main unit 130 (and/or another device) and respond byappropriate programming of probe 100 circuitry, memory-based tables,registers, etc.

It will be appreciated that in an embodiment where probe 100 is to beused in a sterile environment, the use of wireless interface 120 to mainunit 130 may be desirable, as the use of wireless interface 120 avoidsmany of the problems associated with having a physical connectionbetween probe 100 and main unit 130 that passes into and out of asterile field. In other embodiments, certain sheathing or sterilizationtechniques may eliminate or reduce such concerns. In an embodiment wherewireless interface 120 is used, controls 104 may be capable of beingmade sterile so as to enable a treatment provider to use controls 104while performing ultrasound imaging tasks or the like. However, eitherwireless interface 120 or wired interface 122, or a combination of both,may be used in connection with an embodiment.

Probe 100 circuitry also includes power supply 236, which may operate toprovide drive voltage to the transmitters as well as power to otherprobe electronics. Power supply 236 may be any type of electrical powerstorage mechanism, such as one or more batteries or other devices. Inone embodiment, power supply 236 may be capable of providingapproximately 100V DC under typical transmitter load conditions. Powersupply 236 also may also be designed to be small and light enough to fitinside a housing of probe 100, if configured to be hand held by atreatment provider or the like. In addition, power supply managementcircuitry 230 may also be provided to manage the power provided by powersupply 236 to the ultrasound-related circuits of probe 100. Suchmanagement functions include monitoring of voltage status and alerts oflow-voltage conditions, for example.

Controls 104 may be provided to control probe 100. Control interface 232may pass user input received from controls 104 to data/control arbiter228 for processing and action, if necessary. Such control informationmay also be sent to the main unit 130 through either wireless interface120 and/or wired interface 122. In addition to sending data to main unit130, wireless interface 120 may also receive control or otherinformation from main unit 130. This information may include, forexample, image acquisition parameters, look-up tables and programmingcode for field programmable gate arrays (FPGAs) or microcontrollersresiding in probe 100, or the like. Controller interface 232 withinprobe 100 may accept and interpret commands from main unit 130 andconfigure probe 100 circuitry accordingly.

Now that an example configuration of components of probe 100 has beendescribed, an example configuration of components of main unit 130 willbe discussed with reference to FIG. 2. It should be noted that any orall of the components illustrated in FIG. 2 may be disposed within oneor more housings (not shown in FIG. 2) having any form factor.

As discussed above, probe 100 may be in communication with main unit 130by way of wireless interface 120 and/or wired interface 122. It will beappreciated that in an embodiment most data transfer occurs from probe100 to main unit 130, although in some embodiments more data may betransferred from main unit 130 to probe 100. That is, large amounts ofimage data sent from probe 100 may be received by main unit 130, as wellas control information or the like. Control information is managed and,in many cases, generated by Central Processing Unit (CPU) controller332. CPU controller 332 may also be responsible for configuringcircuitry of main unit 130 for an active mode of operation with requiredsetup parameters.

In some embodiments, data/control arbiter 310 may be responsible forextracting control information from the data stream received by wirelessinterface 120 and/or wired interface 122 and passing it to CPU 332 whilesending image data from the data stream to input buffer 312.Data/control arbiter 310 may also receive control information from CPU332, and may transfer the control information to probe 100 via wirelessinterface 120 and/or wired interface 122.

A user, such as a treatment provider or the like, may control theoperations of main unit 130 using control panel 330. Control panel 330may include any type of input or output device, such as knobs,pushbuttons, a keyboard, mouse, and/or trackball, etc. Main unit 130 maybe powered by any type of power supply (not shown in FIG. 2) such as,for example, a 120 VAC outlet along with AC-DC converter module, and/ora battery, etc.

To facilitate forming an image on display 350 (e.g., pixelforming—aprocess that generates an ultrasound image from the image data receivedfrom probe 100), the incoming image data may be stored in,input buffer312. In an embodiment, input buffer 312 may be capable of storing up toapproximately two frames of data, for example, and may operate in a“ping-pong” fashion whereby a previously received frame of data isprocessed by pixelformer 322 while a new incoming frame is written toanother page of memory in input buffer 312. Pixelformer 322 may be anycombination of hardware and/or software that is capable of transformingraw image data received from the receive channels and the transmitevents (e.g., from probe 100) into a pixel-based image format. This maybe performed, in just one example, by coherently combining data fromvarious transmit and receive elements, or groups of elements, to form animage focused optimally at each pixel. Many variations of this approachmay be used in connection with an embodiment. Also, this function mayinclude a beamformer that focuses samples along beam directions. Thefocused sample data may be converted to a Cartesian format for displayon display 350.

Once a frame of complex pixel data has been formed, it may be stored inframe buffer 324 for use by either flow estimator 326 and/or imageprocessor 328. In an embodiment, flow estimator 326 uses, for example,Doppler or cross-correlation methods to determine one or more flowcharacteristics from the received image (e.g., ultrasound echo) data.Once the flow estimation parameters have been computed, they may beencoded into data values and either stored in frame buffer 324 foraccess by image processor 328 and/or sent directly to image processor328. Note that the term “pixel” as used herein typically refers to animage sample, residing on a Cartesian polar and/or non-uniformcoordinate grid, computed by processing captured echo signal data.Actual display pixels may differ from these image pixels in variousways. For example, the display pixels, as presented on display 350, maybe a scaled, resized, filtered, enhanced, or otherwise modified versionof the image pixels referred to herein. These functions may be performedby a processor, for example, image processor 328. Pixel also may referto any finite level, value, or subcomponent of an image. For example, animage that is made up of a number of subcomponents, both visual andotherwise, may be referred to as a pixel.

Spectral Doppler processor (SDP) 320 may receive focused baseband datafrom pixelformer 322 from one or more spatial locations within the imageregion in a periodic or other fashion. The spatial locations may bereferred to as range gates. SDP 320 may perform high-pass filtering onthe data to remove signal contributions from slow moving tissue or thelike. The remaining higher frequency signals from blood flow may be inthe normal audio frequency range and these signals may be conventionallypresented as an audible signal by speaker 318. Such audio informationmay, for example, assist a treatment provider in discerning a nerve froma blood vessel and/or a vein from an artery. SDP 320 may also performspectral analysis via a discrete Fourier transform computation, or othermeans, to create an image representing a continuously updated flowvelocity display (i.e., a time-varying spectrogram of the blood flowsignal). The velocity data may be sent through image processor 328 forfurther processing and display.

A user of main unit 130 may use microphone 314 for controlling main unit130 using, for example, voice recognition technology. Alternately, or inaddition to using microphone 314 for control purposes, a user may usemicrophone 314 for taking notes while examining a patient. Audio notesmay be saved separate from, or along with, video data.

Audio codec 316 may accept audio data input from microphone 314 and mayinterface with CPU 332 so audio data received by audio codec 316 may bestored and/or interpreted by CPU 332. Such audio interpretation mayfacilitate system control by way of, for example, voice commands from auser of main unit 130. For example, frequently-used system commands maybe made available via voice control. Such commands may also be madeavailable by way of control panel 330, for example. Audio storagefacilitates audio annotation of studies for recording patientinformation, physician notes and the like. The audio data may first beconverted to a compressed format such as MP3 before storing in, forexample, storage 338. Other standard, proprietary, compressed oruncompressed formats may also be used in connection with an embodiment.Speaker 318 may provide audio output for reviewing stored annotation orfor user prompts from main unit 130 resulting from error conditions,warnings, notifications, etc. As mentioned above, Doppler signals mayalso be output to speaker 318 for user guidance in range gate and/orsteering line placement and vessel identification.

Video interface 334 may be in communication with image processor 328 todisplay 350 by way of CPU 332. Display 350 may be any device that iscapable of presenting visual information to a user of main unit 130 suchas, for example, an LCD flat panel, CRT monitor, composite video displayor the like. Video data may also be sent to storage 338, which may be aVCR, disk drive, USB drive, CD-ROM, DVD or other storage device. Priorto storage, for example, still image frames of data may be encoded in acompressed format such as JPEG, JPEG2000 or the like. Image clips orsequences may be encoded in a format such as MJPEG, MJPEG2000 or aformat that includes temporal compression such as MPEG. Other standardor proprietary formats may be used as well.

Image processor 328 may accept either complex and/or detected tissueimage data and then filter it temporally (i.e., frame to frame) andspatially to enhance image quality by improving contrast resolution(e.g., by reducing acoustic speckle artifact) and by improving SNR(e.g., by removing random noise). Image processor 328 may also receiveflow data and merge it with such tissue data to create a resultant imagecontaining both tissue and flow information. To accomplish this, imageprocessor 328 may use an arbitration process to determine whether eachpixel includes flow information or tissue information. Tissue and/orflow pixels may also be resized and/or rescaled to fit different pixelgrid dimensions either prior to and/or after arbitration. Pixels mayalso be overwritten by graphical or textual information. In anembodiment, both the flow arbitration and graphical overlay may occurjust prior to image display to allow the tissue and flow images to beprocessed independently.

Temporal filtering typically may be performed on both the tissue andflow data prior to merging the data. Temporal filtering can yieldsignificant improvements in SNR and contrast resolution of the tissueimage and reduced variance of the flow image while still achieving afinal displayed temporal resolution suitable for clinical diagnosis. Asa result, relatively higher levels of synthetic aperture subsampling maybe provided, thereby reducing the required and/or desired number ofreceiver channels (and, consequently, in some embodiments powerconsumption of probe 100). Temporal filtering typically involvesfiltering data from frame to frame using either an FR or IIR-typefilter. In one embodiment, a simple frame averaging method may be usedas discussed below, for example.

Temporal filtering and/or persistence is commonly applied to frames ofultrasound data derived from, for example, tissue echoes. When theacquisition frame rate exceeds the rate of motion of anatomicalstructures, low-pass filtering across frames can reduce random additivenoise while preserving or enhancing image structures. Also, minutedegrees of motion—commonly due to patient or operator movement—help toreduce image speckle, which is caused by the interference of acousticenergy from randomly distributed scatterers that are too small to beresolved with the frequency range of ultrasound probe 100. Speckle iscoherent by its nature so, in the absence of motion, it may produce thesame pseudo-random noise pattern on each image frame. However, smallamounts of motion diversify the speckle enough to make low-passfiltering across frames effective at reducing it.

A simple method of temporal filtering may involve averaging neighboringframes. An example of the recursive version of a moving-average filteris described as follows where X(n) is the input frame acquired at timen, Y(n) is the corresponding output frame, and k is a frame delay factorthat sets the size of the averaging window:

Y(n)=Y(n−1)+X(n)−X(n−k)   (1)

Another simple low-pass filter is a first-order IIR filter of the form:

Y(n)=C×Y(n−1)+(1−C)×X(n)   (2)

In such an embodiment, the coefficient C sets the filter's time constantand the degree of low-pass filtering applied to the frame sequence. Itshould be appreciated that Equations (1) and (2) are just examples ofpossible filters and filtering techniques that may be used in connectionwith an embodiment.

Control panel 330 may provide pushbuttons, knobs, etc., to allow theuser to interact with the system by changing modes, adjusting imagingparameters, and so forth. Control panel 330 may be operatively connectedto CPU 332 by way of, for example, a simple low bandwidth serialinterface or the like. Main unit 130 may also include one or more 1/Ointerfaces 336 for communication with other devices, computers, anetwork or the like by way of a computer interface such as USB, USB2,Ethernet or WiFi wireless networking, for example. Such interfaces allowimage data or reports to be transferred to a computer or externalstorage device (e.g., disk drive, CD-ROM or DVD drive, USB drive, flashmemory, etc.) for later review or archiving, and may allow an externalcomputer or user to control main unit 130 remotely.

There are at least two techniques used for interrogating a medium andprocessing the data needed to create an ultrasound image: synthetictransmit focusing and acoustic transmit focusing. In synthetic transmitfocusing, the interrogating ultrasound waves may be transmitted into themedium, from various locations in the array, in an unfocused ordefocused manner, and reflected waves are received and processed.Somewhat differently, with acoustic transmit focusing the interrogatingultrasound waves may be transmitted in a way that provides focus atcertain spatial locations in the medium, and therefore the transmittedultrasound wave cooperates to form a “beam.” Various embodimentscontemplate synthetic transmit focusing, acoustic transmit focusing,and/or a combination of both. One embodiment contemplates dynamicallyswitching between synthetic transmit focusing and acoustic transmitfocusing modes periodically. For example, color flow data acquisitionmay use acoustic transmit focusing while tissue imaging may usesynthetic transmit focusing. Color flow and tissue data may be collectedon some alternating basis, for example. Other embodiments may includethe use of non-beamformed techniques, in which, a beam may not be formedand/or be partially formed. Similarly, these beamformed andnon-beamformed techniques may be used after the medium is interrogatedin evaluating the echoed ultrasound waves and/or the digital data fromwhich these waves are formed.

FIG. 3 is a block diagram of a system 300 for transmitting an acoustictransmit focusing wave. As shown in FIG. 3, a pulse generator 301provides a signal to a transducer element 302, a transducer element 303,and a transducer element 304. The signal provided by pulse generator 301to transducer element 303 may be provided via a delay module 305.Although not shown in FIG. 3, it should be appreciated that other delaymodules may be provided between other transducers. Also, although justthree transducers are shown in FIG. 3, it should be appreciated thatmany other transducer and arrays of transducers are contemplated in theembodiments.

Each of the transducers may receive the signal via a respective pulsedriver. For example, a pulse driver 306 may be in communication withtransducer element 302, a pulse driver 307 may be in communication withtransducer element 303, and a pulse driver 308 may be in communicationwith transducer element 304. The transducers may be acoustic transducersthat convert the signal provided by pulse generator 301 from anelectrical signal to an acoustic and/or ultrasonic wave. In someembodiments, the size (physical or electrical) of the transducerelements may be sufficiently small to allow the transducer elements toeffectively act as point radiators in a predetermined frequency range.The timing of the pulses provided to the transducers and thus the timingof the acoustic waves created by the transducers may be of any nature,according to the contemplated embodiments. For example, the arrangementmay be a phased array whereby transmit focal points are typicallylocated at equal radial distances from a common vertex. The transmitbeams are usually located at equal angular distances from each other andmay span a total of 90 degrees or more. While the transmit focus istypically located at one point along the beam, echo data is usuallycollected along the entire beam length starting at the vertex and endingat a point corresponding to some maximum imaging depth. At radiallocations other than the transmit focal point, the transmit beamdiverges with the beam becoming increasingly unfocused at radiallocations furthest from the focal point.

The acoustic waves created by the transducers interrogate a particularpoint or target 309 within a medium. Target 309 may be of any size ordimension. In some embodiments, target 309 may be considered to be apoint-reflector, such that its dimensions are relatively small comparedto the wavelength of the ultrasound wave. In this embodiment, the targetmay be considered to effectively be a Dirac delta function in space,such that the reflected echo wave provides a substantial replica of thewave that hits and interrogates target 309.

In just one example, target 309 is some distance “D” from a center lineof transducer element 303. With “c” as the speed of sound, the amount oftime it takes an ultrasound wave to travel from transducer element 303to target 309 is calculated as T=D/c. The distance from transducerelement 304 to target 309 is D+Δ, so Δ is the difference betweentransducer element 304 distance to target 309 and transducer element 303distance to target 309. The time it takes to travel the distance Δ isτ=Δ/c.

In some embodiments, it may be desirable to apply delays between thepulse generator signals and transducer elements for some purpose. Forexample, in one embodiment, it may be desirable to provide delays tocreate a more focused wavefront at a particular point, like target 309.In a focused wavefront, the ultrasound waves generated by eachtransmitting transducer element may sum substantially constructively atone location within the field of view (FOV) and relatively destructivelyat the other locations in the FOV. In this example, it may be thattransducer elements 302 and 304 create their ultrasound waves first intime, followed by transducer element 303 at a time τ later. FIG. 3captures an example of the emitted acoustic waves some time later, forexample, t<T+τ. These waves created by the transducers will converge andconstructively interfere at the focal location, creating a pressure wavethat is the coherent sum of the three transmit waves. The waves will allarrive at the focal point at time t=T+τ. Typically, under normalconditions, at the other points in space, the waves will notconstructively sum.

FIG. 4 is a block diagram of a receive beamformer system. As shown inFIG. 4, target 309 reflects the transmitted ultrasound wave back totransducers 302-304. Although transducers 302-304 are shown as being thesame as the transducers that transmitted the interrogating ultrasoundwave, the embodiments are not so limited. Instead, it should beappreciated that the echo wave may be received by any availabletransducers, including only a portion of the transmitting transducersand/or different transducers. Any combination thereof is contemplated.

As shown in FIG. 4, target 309 reflects at least a portion of thetransmitted ultrasound wave back to the transducers. As a result of thesmaller target dimensions, in this example, the reflected wave issubstantially hemispherical. Although FIG. 4 illustrates the echo wavesas sinusoidal pulses (typical of ultrasound transducers), it should beappreciated that the echo waves contemplated by the embodiments may beof any characteristic. Also, it should be appreciated that the echowaves may have any type of characteristic frequency F_(c), that may bemodulated with an envelope that may be modeled as Gaussian and/or otherwindowing function. For example, where F_(bw) is the bandwidth of themodulation envelope, a fractional bandwidth, F_(bw)/F_(c) may be 50% to70% (at the −6 dB points) for typical transducers.

In this example, at a time 2 T+τ, the reflected acoustic wave reachestransducer element 303. The transducers act to convert the acoustic waveinto electrical energy. Transducer element 303 may provide theelectrical energy signal to an amplifier 402 that amplifiers theelectrical energy signal as required by the remainder of the system. Ata later time, for example, 2 T+2τ, the reflected wave reaches transducerelements 302 and 304.

Transducer elements 302 and 304 convert the acoustic wave intoelectrical energy that is amplified, respectively, by amplifiers 401 and403. The electrical energy provided by the transducers may be eitheranalog or digital signals. Also, the analog electrical signals may beanalog and later converted to digital signals, for example, usinganalog-to-digital (A/D) converters (not shown). Such conversion todigital signals may be accomplished at any point in the system, ascontemplated by the embodiments. Time delay 305 causes a delay in theelectrical signal from amplifier 402, such that the electrical signalsfrom the three amplifiers arrive at a summer 404 substantiallysimultaneously, or at least in close enough proximity of time to allowthe signals to sum constructively. Such time delay may be accomplishedon both analog and digital electrical signals.

Summer 404 adds the three electrical signals, and the summed signal istransmitted to further circuitry (not shown) for further processing andanalysis. For example, in just one embodiment, the summed signal mayhave its magnitude, amplitude and/or phase sent to a processor whodetermines the corresponding values and converts the values into animage value (e.g., brightness). B-Mode typically refers to determiningan image's brightness value based on the amplitude of the summed echosignals near a transmitted center frequency.

Another method for interrogating a medium and processing the data neededto create an ultrasound image involves synthetic transmit focusing. Withsynthetic transmit focusing methods, each pixel of an image may beformed from data acquired by multiple transmit events from variouslocations of the transducers. Generally, with synthetic transmitfocusing, sequentially acquired data sets may be combined to form aresultant image.

On the transmit side of a synthetic transmit focusing system, it may bedesirable to interrogate as broad an area of the medium as possible.Broad interrogation may be accomplished using many techniques.

FIGS. 5A-5C illustrate examples of different possible configurations andtechniques for providing such interrogation. In particular, FIGS. 5A-5Cprovide examples of a transmit pulse or pulses 501, an arrangement orarray of transducer elements 502, an effective aperture 503, and aresultant beam pattern 504. For example, as shown in FIG. 5A,sequentially providing transmit pulses a single transducer element (forexample of an array of transducers) may create a broad beam pattern.Another example shown in FIG. 5B illustrates providing a series oftransmit pulses each to an individual transducer at substantially thesame time. Finally, as shown in FIG. 5C, providing a transmit pulse toeach transducer in a certain sequence may also create a broad beampattern. FIG. 5C provides just one example of a defocused transmit,which may permit greater signal-to-noise ratio (SNR) and bettersensitivity off the center line of the transducer elements. Although thebeam pattern created by FIG. 5B may not be as broad as the example inFIGS. 5A or 5C, it may be sufficient in certain contemplatedembodiments.

FIG. 6 is a block diagram of a synthetic transmit focus ultrasoundsystem 600. As shown in FIG. 6, a target 617 may be interrogated byultrasound waves transmitted from transducers 601-603. Also, the echoultrasound waves reflected from target 617 may be received bytransducers 601-603.

On the transmit side, a pulse generator 616 provides an electricalsignal to a channel selector switch 618. Channel selector switch 618 maybe programmed to direct the signal from pulse generator 616 to each ofpulse drivers 604-606 (and then onto transducers 601-603) at any onetime. As a result, channel selector switch 618 may provide one of manysequenced signals to the transducer elements. Once a signal is sent to atransducer an acoustic or ultrasound wave is created.

The ultrasound wave may hit target 617 or another part of the medium.Certain parts of the ultrasound wave may be reflected to createreflected echo waves. Certain parts of the reflected ultrasound wavesmay return to one or more of transducer elements 601-603 and/or to othertransducer elements (not shown). The reflected echo wave or waves may beconverted by transducer elements 601-603 or the other transducerelements into an electrical signal. The electrical signal may beprovided to one of receive amplifiers 607-609, depending upon whichtransducer element the ultrasound wave is received. Each amplifier607-609 may provide the electrical signal to a respective A/D converter610-612, which converts the analog signals from each receiver amplifier607-609 to a digital signal.

The digital signal may then be stored in a respective channel memorydevice 613-615. By storing digital data in channel memory devices613-615, subsequent processing may be performed on the data. Forexample, in just one embodiment, the digital data may be processed toidentify the characteristics of target 617 or of any other location inthe medium. Because the digital data is stored with its correspondingparameters, the digital data may be used to identify any point in themedium. This processing is not limited to being performed immediatelyafter receiving the digital data, but may be conducted at some timesubstantially after the digital data is received in channel memorydevices 613-615.

In some embodiments (e.g., a wireless probe), it may be desirable tooperate certain components intermittently. This may be desirable, forexample, to conserve power consumption and/or to reduce overallmaintenance. For example, in some embodiments, A/D converters 610-612may be turned off and on as needed. For example, A/D converters 610-612may operate just long enough so that energy from a particular transducerelement 601-603 has sufficient time to propagate out to the desiredportions of the medium, reflect back from these portions, and return toa transducer element 601-603. After this is accomplished in someembodiments, A/D converters 610-612 may be disabled and/or placed in alow-power state. In other embodiments, (e.g., wired probe that receivespower from a main unit) it may not be necessary to turn off A/Dconverters 610-612, or any other component.

FIG. 7 provides an example illustration of signals transmitted from eachof transducer elements 601603 and received back on respective transducerelements 601-603 and stored in channel memory devices 613-621. It shouldbe appreciated that although just three transducer elements and channelmemory devices are described, either one or many of such components maybe used. Three of such devices are described merely to provide clarityof explanation with brevity.

FIG. 7 illustrates each of transducer elements 601-603 separatelytransmitting an ultrasound wave that is received on each of transducerelements 601-603. For example, as shown in FIG. 7, transducer element601 may transmit an ultrasound wave that is received by transducerelement 601 and stored in channel memory device 613 as echo wave 701.Similarly, for example, transducer element 601 may transmit anultrasound wave that is received by transducer element 602 and stored inchannel memory device 614 as echo wave 702. In addition, transducerelement 601 may transmit an ultrasound wave that is received bytransducer element 603 and stored in channel memory device 615 as echowave 703. Also, with respect to an ultrasound wave transmitted fromtransducer element 602, echo wave 704 may be stored in channel memorydevice 616, echo wave 705 may be stored in channel memory device 617,and echo wave 706 may be stored in channel memory device 618. Withrespect to an ultrasound wave transmitted from transducer element 603,echo wave 707 may be stored in channel memory device 619, echo wave 708may be stored in channel memory device 620, and echo wave 709 may bereceived on channel memory device 621.

In this one example embodiment, there may be nine echo waves 701-709.Echo waves 701-709 each serve as a sequence of data points, representingreflection of a transmitted ultrasound wave from various points in themedium. For example, each data point may be stored in a predeterminedlocation, so as to later identify the data point for subsequentprocessing. Each data sequence is acquired by sampling the reflectedecho waves 701-709 beginning at a time 0 and ending at a time greaterthan 2 T+2τ. If a distance from target 617 to transducer element 602 isD, then a distance from transducer element 601 to target 617 may beconsidered to be D+Δ. A round trip distance (i.e., from transducerelement 601 to target 617 and back to transducer element 601) may berepresented as 2D+2Δ, and a corresponding round trip time may beconsidered to be 2 T+2τ.

For example, for an ultrasound wave transmitted from transducer element601 and received by transducer element 602, echo wave 702, a peak value710 may be found at time 2 T+τ. Similarly, as shown in FIG. 7, the echopulses add coherently for the round trip distances and/or times for theother transmit/receive transducer element pairs. Also, in someembodiments, the coherent adding may not occur at any other point inspace. As a result, the received data points may be syntheticallyfocused or added mathematically by, for example, superposition of theecho data. This may be accomplished in addition to or in lieu ofanalysis and processing of physical acoustic pressure summation in theimage field.

As a result of not simply separating transmit and receive focus, it ispossible to also process transmit and receive delays to synthesize around-trip focus at any point of interest. Yet, it should be appreciatedthat in some embodiments, it may be desirable to also decompose thefocusing into transmit and receive components in addition to or in lieuof the synthetic transmit focusing techniques. For example, it should beappreciated that it may be desirable to treat a one-way time from atransmit transducer element to a target as transmit focusing, and treata one-way time from the target to the receive transducer element asreceive focusing.

Also, synthetic transmit focusing used with or without acoustic transmitfocus techniques may permit improved transmit focus throughout the imagefield. For example, because transmit focusing may at least in part becreated via mathematical summation, focusing may be performed at amultitude of depths within the medium (e.g., each image pixel location),instead of or in addition to a limited number of discrete focal points.This may be accomplished, in some embodiments, by computing round tripdistances and/or times for any point in the image field and summing orprocessing the data samples corresponding to that point from manytransmit/receive combinations to synthesize a focus at the particularpoint. For example, in just one embodiment a focus may be synthesizedfor a particular point in the medium by computing a round trip distanceand/or time from each transmit transducer element to the target and backto each receive transducer element (e.g., for three transmit transducerelements and three receiver transducer elements, there may be ninetransmit/receive pairs as shown in FIG. 7). A processor may then extractfrom a predetermined database and/or data store (e.g., channel memorydevices 613-621) certain data points that correspond to those round-tripdistances and/or times. These data points may then be summed, forexample, or processed in some way to permit image formation.

Synthetic transmit focusing and/or partial synthetic transmit focusingtechniques may require additional considerations when substantiallysignificant image motion is present. Consequently, in some embodiments,the synthetic transmit focusing or partial synthetic transmit focusingtechniques may use methods and techniques to track movement of themedium. For example, in embodiments where the transmit transducerelements fire sequentially, the echoes from targets in the medium may becollected over a period of time. If the targets move during the timeperiod, the distance and/or time data of the echo waves may be changedfrom one interval to the next. As a result, spatial and contrastresolution of the image may be degraded. Although movement of the mediumdoes not minimize the utility of the suggested techniques, it may bedesirable in some embodiment to track, and perhaps even correct for suchmovement. Alternatively, some embodiments may restrict the medium suchthat movement does not occur. Also, some embodiments may decrease theacquisition interval and reduce the time of acquisition, thus reducingthe likelihood of movement during the shorter acquisition period. Also,in some embodiments a number of transmit elements may be reduced inresponse to detected motion, thus reducing the acquisition time and theeffect of motion on the resulting image.

Some embodiments may quantify signal-to-noise ratio (SNR). For example,assuming M receive transducer elements and N transmit transducerelements, and a receive channel noise floor of e_(n); if the system isusing acoustic transmit focusing techniques, then the acoustic echoinformation from the selected beam direction may be acquired in a singletransmit event, so the receive beamformer has M*e_(n) of noise in itsoutput. This is due in part to each receive transducer elementcontributing its noise floor to the output sum. With the synthetictransmit focusing techniques, there is M*N*e_(n) of noise in the output,because each receive transducer element adds noise to a data record eachtime echo data is captured from a transmit transducer element. In otherwords, each receive transducer element runs N times (e.g., sequentially)to capture the data from the transmit transducer elements. This may bedifferent than some embodiments that use acoustic transmit focusingtechniques, where the signals from the transmit transducer elements arereturning at substantially the same time, and therefore may be capturedin substantially one pass.

It should be appreciated that some embodiments contemplate the use of areduced redundancy array of transducer elements. For example, anN-element phased array system typically has N² transmit/receivetransducer element combinations. In some embodiments, almost half of thecombinations may be redundant or otherwise unnecessary. In theembodiments that employ a reduced redundancy array of transducerelements, certain transmit/receive transducer element combinations maybe ignored or otherwise decimated in some manner.

Reduced redundancy arrays may be accomplished using a number oftechniques. For example, some embodiments may employ transmitting from agroup of transmit transducer elements substantially simultaneously,instead of or in addition to using a single element for each transmitevent. Also, in some embodiments, increasing the spacing of the transmittransducer elements and/or element groups reduces a number of transmitevents for each image frame. This may permit a greater frame rate and/ora reduced computation rate in the image processing. Some embodiments mayreduce redundancy by turning off certain transmit transducer elements.This may be accomplished on successive transmit events, where each eventis constrained to elements nearby the transmitted group. Those skilledin the art may refer to such techniques as Multi-element SyntheticAperture Focusing (MSAF). Other sparse array and synthetic focusingmethods are also contemplated embodiments.

In some embodiments the transmit/receive transducer elements may be usedin groups that may or may not be overlapping. Overlappingtransmit/receive transducer element groups may facilitate the use oflower voltages to drive the transmitter transducer elements.Alternatively, in some embodiments, using the same voltage to drive agroup of transmitter transducer elements may provide greater transmitpower than may be achieved by driving a single element, for example.

Synthetic transmit focus techniques may allow some embodiments to reducea number of required element transmit events per image frame. Such areduction may allow for a relative increase in the power efficiency, andtherefore improve self-powered considerations, like the operational timeof a battery and/or battery size.

Some embodiments may use a single transmit transducer element to createperhaps a less directional ultrasound wavefront, and/or a wavefront thatbetter approximates a point source (e.g., a hemispheric wavefront). Asdiscussed with reference to FIGS. 5A-5C, an element group firedsubstantially simultaneously may produce a plane wave. Yet, in someembodiments, it may be desirable to have either a plane wave and/or areasonably hemispheric wave. For example, the hemispheric wave maypermit the received echo waves to interrogate a larger portion of themedium. For a group of transducer transmit elements, a defocusedwavefront may emulate a point source that is synthesized by properdefocusing of the transmit beam. This technique may permit greatertransmitted energy with lower drive voltages while also producing a lessdirectional wavefront.

FIG. 8 illustrates just one example technique of decimating the numberof transducer elements 805 that receive the echo ultrasound wave. Asshown in FIG. 8, a transmitting transducer element 801 may transmit froma single transducer element and be received on less than a total numberof available transducer receiver elements 802. In the example of FIG. 8,there are nine receive transducer elements 802 (shown shaded) availableto receive the reflected echo wave. In some embodiments, the availablereceiving transducer elements may vary depending upon a particulartransmitting transducer element and/or the location of the target, forexample. The receive transducer elements may be changed to a differentpattern of elements, for example, to accommodate the transducer edges.

Image formation involving acoustic transmit focus techniques involvesthe use of a scan line that often is perpendicular to the tangent oftransmitting transducer array. The scan line may also be steered atdifferent angles using phased array techniques, well known to thoseskilled in the art. Typically, the scan lines are acquired sequentiallybeginning at one end of an image frame and continuing throughout theframe. However, in some embodiments, samples along the scan lines do notnecessarily align with the pixels on a Cartesian grid. With respect to aphased array system, the scan line sample density may be non-uniformlydistributed throughout the image frame with a higher density of samplesoccurring in the near-field. Scan lines may then be processed to allowconversion to an image Cartesian format. For example, with B-Modeimaging, well known to those skilled in the art, processing may involvemagnitude detection, log compression, spatial and temporal filtering,for example. A two-dimensional interpolation method (e.g., bilinearinterpolation) may then be performed to convert to the Cartesian imageformat.

The disclosed embodiments contemplate using image processing techniquesconvenient for acoustic transmit focusing. Also, with respect tosynthetic transmit focusing methods, the disclosed embodimentscontemplate using additional image processing techniques. For example,in some embodiments, synthetic transmit focusing techniques may formimage pixels directly and/or indirectly from collected data samples. Onesuch technique employs coherent summation of the signal samples fromeach transmit/receive pair of array elements for each pixel.

With acoustic transmit focusing, it may be that samples along the beammay not line up with image pixels. As a result, interpolation of thebeam samples may be required to compute and determine the precise pixelvalue. In some embodiments, the beam sample may align with the imagepixel and thus no interpolation may be necessary.

With synthetic transmit focusing techniques, each pixel may be able tobe formed from the collected data values determined for each part of themedium. In particular, with synthetic transmit focusing because eachpixel has its own receive path and is formed by combining signals frommultiple transmit transducer elements and receive transducer elementpairs, it may not be necessary to conduct scan conversion or processing.In other words, because synthetic transmit focus techniques provide bothtransmit and receive dynamic focusing capability, the formation of thepixels of the corresponding image may be determined directly from theroundtrip paths from transmit transducer elements to the target (orpixel) and back to receive transducer elements. Therefore, forming apixel on an image derives from synthetic transmit focusing because eachpixel can be ideally focused on both transmit and receive.

Some embodiments may provide acoustic transmit focusing techniques andsynthetic transmit focusing techniques simultaneously for combinationmodes that may require both techniques such as color flow, for example.Some embodiments may alternate between acoustic transmit focusing andsynthetic transmit focusing techniques dynamically and, perhaps, on aperiodic basis. A variety of other combinations of acoustic transmitfocusing and synthetic transmit focusing techniques are contemplated bythe disclosed embodiments.

In some embodiments, received echo signals may be substantiallysimultaneously acquired from all, or part, of the transducer elementarray, for example, on each transmit event. Some embodiments may createeach pixel by time and amplitude adjustments for each transmit andreceive transducer element pairing. Also, time delay resolution may beimproved by using interpolation techniques among the received datasamples (e.g., linear interpolation between sample pairs in Cartesianspace and/or polar space, spline, non-linear interpolation, and thelike).

Although, it may not always be possible to accomplish such direct pixelformation with acoustic transmit focusing techniques, it should beappreciated that such pixel forming techniques may be used. Also, suchpixel forming techniques may be used in combination with data sampleinterpolation techniques. In addition, with synthetic transmit focusmethods, both pixel forming techniques and interpolation techniques maybe used to create an image from the data points.

In some embodiments, it may be that all of the availabletransmit/receive transducer element pairs are used to create the pixel.The following equation is one example of how to determine the datasample index (n) for a single transmit/receive transducer element pair:

n=F _(S) ×c×{SQRT((X _(P) −X _(T))²+(Y _(P) −Y _(T))²)+SQRT((X _(P) −X_(R))²+(Y _(P) −Y _(R))²)}

The variables X_(P) and Y_(P) are the coordinate dimensions of the pixelto be formed. The variables X_(R) and Y_(R) are the coordinatedimensions of the receive transducer element and the variables X_(T) andY_(T) are the coordinate dimensions of the transmit transducer elementor virtual center of a group of transmit elements. The variables F_(S)and c are the data sampling rate and the speed of sound in tissue(typically 1540 m/s), respectively. This calculation may be performedfor each transmit/receive element transducer pair contributing to eachpixel. Note that for a linear array, Y_(R) is zero. The disclosedembodiments also contemplate that such synthetic focusing techniques canbe readily extended to three dimensions, as is well understood by thoseskilled in the art.

The first part of the equation relates to dynamic transmit focusing andthe second part dynamic receive focusing. In the case of a fixedacoustic transmit focus system, the origin of the transmit beam is fixedat (X_(T), Y_(T)) for samples and/or pixels formed from that transmitevent. If receive beams are formed, the equation simplifies furtherbecause the distance along the beam vector is merely proportional to thesample count of the vector. Therefore, for an acoustic transmit focusingsystem, the equation above reduces to the following, with D representingthe radial distance along the beam:

n=F _(S) ×S×{D+SQRT((X _(P) −X _(R))²+(Y _(P) −Y _(R))²)}

Note that in this case, X_(P) and Y_(P) are the coordinate dimensions ofsamples along the beam. If the transmit and receive beam origins are thesame, the equation may be expressed as follows with Θ representing thebeam angle relative to the horizontal axis along the array dimension:

n=F _(S) ×S×{D+SQRT((D×cos(Θ)−X _(R))²+(D×sin(Θ)−Y _(R))²)}

For T transmitter elements and R receiver elements, the number of suchcalculations per output pixel in a synthetic transmit focusing systemmay be proportional to the product of T and R. Also, a number ofcalculations required in an acoustic transmit focusing system to computesamples along the beam may be proportional to R.

In some embodiments, the computing complexity necessary to accomplishthe synthetic transmit focusing techniques may be greater. For example,consider a linear transducer array probe with N transducer elements. Ifeach column of pixels in the image is made to align with the center ofeach transducer element in the array, there may be as many beams astransducer elements. With respect to synthetic transmit focusingtechniques, transmitting on the transducer elements in the arrayindividually may require N transmissions to create an image frame. Withrespect to acoustic transmit focusing techniques, it may be assumed thatan equal number of transducer transmissions may be required if there isone transmission per beam. If beam samples are made to align with imagepixels, signals from R receive elements may be combined to form eachsample or pixel per beam.

Therefore, for the synthetic transmit focusing techniques, N×R signalcombinations per pixel may be required, and thus in just someembodiments the computational requirements of synthetic transmitfocusing system may be N times greater than the acoustic transmitfocusing system. Due to the potential increased computational burden ofsynthetic transmit focusing, in some embodiments, it may be desirable toselect and limit the number of transmit/receive transducer element pairs(T×R) necessary to form each pixel. This may be accomplished by aperturerestricting criteria known in the art as f-number and/or acceptanceangle. In addition, maximum transmit/receive aperture sizes that aresmaller than the full array may be enforced.

Some embodiments may use interpolation (e.g., linear and/or sample) aswell as demodulation techniques, like using quadrature-sampled basebanddata with phase adjustment. It should be appreciated that thesetechniques may be used with synthetic transmit focusing techniques,acoustic transmit focusing techniques, and any combinations thereof.Also, these example techniques are not inclusive, but it should beappreciated that alternative methods of demodulation and interpolation,perhaps with appropriate phase adjustment, are contemplated by thedisclosed embodiments. In addition, compensation techniques may be usedto preserve coherence.

In some embodiments, echo signals received by the receive transducerelements may be characterized by a carrier frequency Fc (with an angularfrequency of Wc=2πFc), modulated by a pulse envelope where thefractional bandwidth is typically 50% to 70% (at −6 dB). In someembodiments, it may be desirable to quadrature demodulate the receivedecho signals to extract a modulation envelope. With quadraturedemodulation, resulting baseband analytic pair signals (e.g., I+jQ) mayinclude information from the original modulation signal. As a result,having the demodulation frequency, and the modulation signal (I+jQ),permits the echo signals to be recreated, which may be desirable in someembodiments.

In some embodiments, for example where a lower data rate is desired,baseband sampling techniques may be employed. In some embodiments, ifthe baseband analytic pair includes the modulation information that wasin the original echo signals, the data may be used for acoustic transmitfocusing and/or synthetic transmit focusing techniques, instead of, orin addition to, recreating the original echo signals before beamforming.In either case, in using the baseband analytic pair with respect toacoustic transmit focusing, partial acoustic transmit focusing, and/orsynthetic transmit focusing, the data consequent from the demodulationprocess that is included with the baseband signals may be accounted forin some embodiments. In addition, in some embodiments, carrier frequencyinformation may be accounted for as well. Accounting for theseadditional considerations may be accomplished in any of the disclosedembodiments, including acoustic transmit focusing and synthetic transmitfocus techniques, for example.

Considering the example described with respect to FIG. 7, round-triptime from transducer element 602 to the target and back to transducerelement 602 is 2 T, and round-trip time from transducer element 602 tothe target and back to transducer element 601 is 2 T+τ. As discussed,the signals will have phase coherence and add constructively. Using thisexample and applying it to demodulation prior to acoustic transmitfocusing and/or synthetic transmit focusing, may provide the following:x(t)=M(t)Fc(t), where x(t) is the round-trip impulse response of thetransducer elements, M(t)=Mi(t)+jMq(t) is the modulation envelope of theround-trip impulse response, and C(t)=sin(Wc t) where Wc is thecharacteristic center frequency of the particular transducer element. Itshould be appreciated that a round trip impulse response of thetransducer element may be two passes through the element's one-wayimpulse response. Therefore, a round-trip impulse response may be theself-convolution of the one-way impulse response. The echo signals e(t)from the target can be written as follows:

Echo from transmit on transducer element 602, received on transducerelement 602:

e ₂₂(t)=M(t−2 T)C(t−2 T),=Mi(t−2 T)sin(Wc(t−2 T))+j Mq(t−2 T)sin(Wc(t−2T))

Echo from transmit on transducer element 602, received on transducerelement 601:

e ₂₁(t)=Mi(t−(2 T+τ.)sin(Wc(t−(2 T+τ))+j Mq(t−(2 T+τ.)sin(Wc(t−(2 T+τ.))

As discussed, quadrature demodulation may be used on the received echosignals. In these embodiments, using quadrature demodulation, each echosignal may be multiplied by an in-phase and a quadrature sine wave toget two baseband components. For the echo from transmit on transducerelement 602, received on transducer element 602, the following:

d _(i22)(t)=sin(Wct)e ₂₂(t)=sin(Wct)Mi(t−2 T)sin(Wct−Wc(2 T))+jsin(Wct)Mq(t−2 T)sin(Wct−Wc(2 T))

and

d _(q22)(t)=cos(Wct)e ₂₂(t)=cos(Wct)Mi(t−2 T)sin(Wct−Wc(2 T))+jcos(Wct)Mq(t−2 T)sin(Wct−Wc(2 T))

Where the analytic baseband signal d₂₂(t)=d_(i22)(t)+j d_(q22)(t)

Using the trigonometric relations sin(a)sin(b)=½[cos(a−b)−cos(a+b)] andcos(a)sin(b)=½[sin(a+b)−sin(a−b)], provides:

d _(i22)(t)=½{Mi(t−2 T)[cos(Wc(2 T))−cos(2Wct−Wc(2 T))]+j Mq(t−2T)[cos(Wc(2 T))−cos(2Wct−Wc(2 T))]}

In some embodiments, it may be desirable to look just at the basebandcomponent. In these embodiments, it may be desirable to filter thecos(2Wct−Wc(2 T)) term, which represents a twice frequency (2Fc)component, and setting this term to zero, provides:

d _(i22)(t)=½{Mi(t−2 T)cos(Wc(2 T))+j Mq(t−2 T)cos(Wc(2 T))}

Using the other substitution and lowpass filtering for the quadraturecomponent gives the following:

d _(q22)(t)=−½{Mi(t−2 T)sin(Wc(2 T))+j Mq(t−2 T)sin(Wc(2 T))}

and the analytic baseband signal is:

d ₂₂(t)=½{[Mi(t−2 T)+j Mq(t−2 T)]*[cos(Wc(2 T))−j sin(Wc(2 T))]}=½M(t−2T)e ^(j Wc 2 T)

This expression provides the original envelope information (e.g., M(t−2T)), and also includes a residual demodulator phase term (e^(j Wc 2 T)).The residual demodulator phase term is present because the phase of thedemodulator signals at that point in time phase rotates the envelopefunction by some amount. In other words, the phase rotation isessentially random because there typically is no relationship betweenthe round-trip times and the demodulator signal phase. In someembodiments, the random phase rotation may be acceptable because inthose embodiments, phase term may not impact the imaging process. Forexample, with respect to beamformed techniques, B-Mode techniques thatrespond to amplitude, and Doppler mode techniques that analyze phasechange with respect to time, absolute phase values may not be required.

Similarly, for the echo from transmit on transducer element 602,received on transducer element 601, the following:

d ₂₁(t)=½M(t−(2 T+τ))e ^(j Wc(2 T+τ))

Accomplishing synthetic transmit focus techniques with the basebandcomponents advances the d₂₂(t) signal by 2 T, and advances the d₂₁(t)signal by 2 T+τ. Summing these terms along with contributions from theother transmit/receive transducer element pairs for the target, providesthe following:

pd=Σ _(n=1 . . . 3)Σ_(m=1 . . . 3) d(t _(round trip))=d ₂₁(2 T+τ)+d ₂₂(2T)+seven other terms.

The variable pd represents pixel data summation over thetransmit/receive transducer element pairs at the target.

In the synthetic transmit focus example, the demodulator phase term mayrepresents a phase error between the two signals that needs correctionor compensation, in some embodiments. This is due, in part, to the factthat modulation envelope M(t) components are phased aligned, but not thedemodulator phase terms, because the demodulator phase term may nolonger be a function of time.

The disclosed embodiments contemplate many ways to compensate for thedemodulator phase term. One example technique for compensating fordemodulator phase term contemplates applying an additional phaserotation term to d₂₁(t) to account for a later arrival time of thesignal on transducer element 601. By considering the difference in thetimes of flight of the two signals, it may be appropriate to apply aphase rotation of e^(−j Wc τ) to d₂₁ to achieve phase alignment of d₂₁and d₂₂. In some embodiments, a similar phase adjustment may be appliedto the other transmit/receive transducer element pairs to phase alignthem to d₂₂(t) before summing to get pd.

In implementing the above technique, in some embodiments the phaserotation correction that may need to be applied to the baseband signalsbefore summation may need to be the modulo-2π remainder of the totalphase error. For example, assuming the same signals derived ford_(nm)(t) as above, and sampling at a demodulator frequency with afractional bandwidth of the echo signals less than 100%, the demodulated(baseband) signal bandwidth may be less than ½ the demodulatorfrequency. Therefore, the signals may be adequately sampled, at least inaccordance with Nyquist criterion, well known to those skilled in theart. If a sample clock is chosen to sample at zero phase of thedemodulation signal, then the D samples may have zero phase relative tothe demodulator signal. Therefore, calculating the pixel data sum pdusing the nearest-neighbor samples (i.e., sample nearest to the actualround-trip time for that transmit/receive transducer element pair) mayeliminate any differential demodulator phase error between signals inthe summation, because the modulo-2π phases of the data points in thesummation would be zero.

In some embodiments, where interpolation between adjacent samples isused, it may be advisable to use a “fractional time” between samples todetermine a quantity of additional phase shift to apply to equalize theinterpolated sample to zero phase. The modulo-2π remainder of the phaseerror is 2π times the “fractional time” between actual samples, and thesampling process gives a phase reference of the demodulator, the phaseis at zero at the sample times, and it traverses 2π: between thesamples.

A sampled version of the demodulated echo signals may be represented asds_(nm), with ds_(nm)(t₀) as the digitally sampled demodulated echosignal falling at (continuous time) t₀, and ignoring quantizationeffects provides ds_(nm)(t₀)=d_(nm)(t₀). Assuming that one of the sampletimes is at 2 T, then ds₂₂(2 T) is one of the stored samples fromtransducer element 602. Because the time 2 T is at the sample time, thedemodulator phase at that moment is an integer multiple of 2π. The phaseterm of d₂₂(2 T) is e^(jn2π)=1, the expression for d₂₂(2 T) becomes:

ds ₂₂(2 T)=d ₂₂(2 T)=½[Mi(0)+j Mq(0)], with M(0) decomposed intoanalytic pair

Evaluating d₂₁(2 T+τ) by decomposing T into an integer number of sampletimes and a remainder part, as follows:

-   -   n_(τ)=int(τ Fc) where int( ) denotes the integer part operator        then    -   τ_(int)=n_(τ)/Fc is the time that corresponds to an integer        number of sample cycles. and:    -   τ_(rem)=τ−n_(τ)/Fc is the time remainder

So that:

τ=τ_(int)+τ_(rem)

Defining fractional time τ_(frac)=τ_(rem)Fc; 0≦τ_(frac)<1, whereτ_(frac) is the “fractional time” or fraction of the sample intervalbetween these samples where the actual time of flight falls, theexpression can be written for T as follows:

τ=τ_(jnt)+τ_(frac) /Fc

The sample times substantially immediately before and substantiallyimmediately after the time 2 T+τ are:

t=2 T+τ_(jht) and t=2 T+τ_(jht)+1/Fc

substituting τ_(int)=τ−τ_(rem) gives 2 T+τ_(int)=2 T+τ−τ_(rem) and

2 T+τ_(int)+1/Fc=2 T+τ+(1/Fc−τ _(rem)) so:

ds ₂₁(2 T+τ_(int))=d ₂₁(2 T+τ−τ_(rem))=½[Mi(−τ_(rem))+j Mq(−τ_(rem))]and

ds ₂₁(2 T+τ_(int)+1/Fc)=d ₂₁(2 T+τ+(1/Fc−τ _(rem)))=½[Mi(1/Fc−τ_(rem))+j Mq(1/Fc−τ _(rem))]

Again, the phase terms are eliminated because the phase is a multiple of2τ at the sample points.

Using linear interpolation between the samples gives an approximation ofthe I and Q components of d₂₁(2 T+τ). Also, applying a negative phaseshift proportional to the fractional time interpolation cancels theadditional phase rotation from the differential time component τ. Theinterpolated (computed) value result is ds₂₁ intp (2 T+τ) is as follows:

ds _(21 interp)(2 T+τ)=[τ_(frac)(ds ₂₁(2 T+τ_(int)+1/Fc))+(1−τ_(frac)()ds ₂₁(2 T+τ_(int)))]e ^(−j2πτfrac)

Notably, the expression varies as a function of τ_(frac) and the twosamples. The linear interpolation into the I and Q components of the A/Dsamples yields:

ds_(21 interp)(2 T+τ)≅¼[τ_(frac) Mi(1/Fc−τ_(rem))+(1−τ_(frac))Mi(−τ_(rem))+jτ _(frac) Mq(1/Fc−τ_(rem))+j(1−τ_(frac))Mq(−τ_(rem))]e ^(−j2πτfrac)

The expression shows the sample times and constituent signal componentsfrom the input signal that are represented in the interpolated datapoint. Forming the pixel data sum provides:

pd=Σ _(n=1 . . . 3)Σ_(m=1 . . . 3)ds_(nm)(t _(round trip))=ds ₂₂(2 T)+ds_(21 interp)(2 T+τ)+7 other interpolated terms.

There is no loss of generality by assuming that 2 T was a sample time,because the other terms in the expression for pd need to be interpolatedto align with this arbitrary phase choice. The phase of the demodulatorsignals is essentially random with respect to any given pixel locationon the screen for any given transmit/receive transducer element pairbecause the round-trip time for each transmit/receive transducer elementpair to each pixel in the image area may be different. In other words,the demodulator signal phase typically does not align precisely withmore than one sample point for one transmit/receive transducer elementpair at a pixel location in the image area. In some embodiments,arranging the demodulator signals may yield an advantage becauseinterpolation and phase adjustment typically will be done on manysamples used to create the pixel data.

For linear interpolation, the above may be decomposed into an operationon each of the adjacent sample points. For example, for the A/D samplepoint prior to the round-trip time, multiplication of the data point isby the factor (1−τ_(frac))e^(−2πτfrac), and for the data point followingthe round-trip time, multiplication of the data point is by the factor(τ_(frac))e^(−j2πτfrac).

In some embodiments, it may be desirable to convert to Cartesiannotation, for example, to implement in conventionalmultiply-accumulators (MACCs). Generalizing the resulting operations onthe sample data as a series of complex multiply-accumulations to formthe pixel data point, as follows:

pd=Σ _(n=1 . . . 3)Σ_(m=1 . . . 3)Σ_(t−, t+) ds _(nm)(t)

t− and t+ refer to the sample points preceding and following thecomputed round trip time.

ds_(nm)(t) may be expressed as the complex multiplication(a+jb)(d_(i)(t)+j d_(q)(t)), where the term (a+jb) is the Cartesianconversion of the fractional time weighting and phase correction factorand the terms d_(i)(t) and d_(q)(t) are the in-phase and quadraturesignal components at time (t) as defined previously. For example, forthe data sample from time t+,

a=τ _(frac) cos(−2ττ_(frac)) and b=τ _(frac) sin(−2ττ_(frac))

And for the data sample from time t−,

a=(1−τ_(frac))cos(−2ττ_(frac)) and b=(1−τ_(frac))sin(−2ττ_(frac))

In some embodiments, each complex multiplication may require fourmultiply-accumulate (MACC) operations. Therefore, linear interpolationbetween samples with phase adjustment may require as many as 8 MACCoperations per transmit/receive transducer element pair in the pixelsummation. Also, coefficients a and b may include amplitude weighting tocorrect for signal path attenuation and element factor and/or to achievea desired array apodization. These factors may impact the system's pointspread function, which may be fine-tuned by appropriate amplitudeweighting of the signals from each element for a given point in space(i.e., per pixel). In some embodiments, amplitude weighting may be usedto adjust the point spread function for each pixel individually, forexample. Also, some embodiments may use linear interpolation onquadrature-sampled baseband data with the described phase adjustmenttechnique. Of course, it should be appreciated that the embodiments arenot so limited and that various other methods of demodulation andinterpolation with appropriate phase adjustment are contemplated by thedisclosed embodiments.

Certain embodiments may accommodate other types of distortions. Forexample, motion of the target or medium may introduce a form of phasedistortion. These motion or movement errors may be due to the relativelylarge time interval over which the data is acquired and coherentlycombined. Typically, the degree of distortion may be proportional to therate of motion and the length of the acquisition time interval. One suchexample of a system that collects the data over a large time interval isthe synthetic transmit focus technique. This distortion may be inaddition to the phase distortion discussed.

In some embodiments, the motion distortion may be accommodated orcorrected using a variety of techniques. For example, reducing aredundancy in an array reduces a number of transmit events necessary toacquire a frame of data, and thus mitigates the likelihood of movement.Constraining the subset of transmit and/or receive transducer elementsto a subset of the array may also reduce phase distortion due to motion,albeit perhaps at the expense of reduced lateral resolution and SNR insome embodiments.

Decimating or reducing certain ultrasound transducers from receivingand/or transmitting ultrasound waves also may reduce transmitted databandwidth. Such reduction may be accomplished on beamformed, partiallybeamformed and non-beamformed techniques. Also, by reducing a data atthe beginning of the system, further reductions may be achieved, likememory and processing concerns. The decimation of the ultrasoundtransducers may be accomplished based on a number of considerations,like a region of interest, where the region of interest is a function ofa displayed image. Also, the decimation may be based on a displayresolution of an image frame, a rate of the transmission of the digitaldata, and a displayed region of interest of the medium. The decimationmay be varied as a function of a capability of a remote unit, quality oftransmission of digital data, quantity of errors in transmission ofdigital data, and availability of power, for example.

Also, correcting phase errors in Multi-element Synthetic ApertureSystems, well known to those skilled in the art, using cross-correlationprocessing also are contemplated by the disclosed embodiments. Suchcross-correlation techniques may correct for phase errors due to eithertissue motion and/or to tissue inhomogeneities. In some embodiments,adaptive correction may require greater computational complexity. Insome embodiments, it may be desirable to reduce such complexity whilestill providing correction. One technique of reducing the complexity maybe to constrain the correlation to a region of interest. This region ofinterest may be determined, for example, by a user. For an image that isrelatively stationary and/or homogeneous, and has small regions ofmotion, such a technique may be satisfactory in some embodiments.

Other target and/or tissue motion may occur due to operator movement andmay be relatively intermittent. This motion may be corrected and/oraccommodated by detecting the presence of motion, quantifying it by a“motion factor”, and adapting to it by changing acquisition parameters.Such changing acquisition parameters may trade off image quality foracquisition speed, in some embodiments. For example, such changingacquisition parameters may include adjustment of image acquisitionparameters such as maximum transmit or receive aperture size, f-number,acceptance angle, aperture sparsity, etc. It should be appreciated thatthe motion factor may also be used to adjust non-coherent processingparameters such as frame averaging or persistence commonly applied todetected B-Mode image data. While in some embodiments not as susceptibleto motion as coherent processing, frame averaging also produces poorresults due to a high rate of tissue motion, which may be acceptable insome embodiments.

In a probe environment, there may be a wired or wireless communicationchannel between the probe and the main unit. With regard to ultrasoundimaging, the communication channel typically should be able to handlehigh transmission rates and have relatively large data bandwidth. Also,because of the nature of the ultrasound device in medical settings, thecommunication channel may be sufficiently robust and provide relativeimmunity from interference of nearby wireless devices, and randomelectromagnetic noise. In addition, the communication channel may permitthe main unit to communicate with and be operable with other wirelessand wired probes and systems. For example, the main unit may be able todistinguish certain probes from other probes within proximity.

The communication channels may include more than one channel to increasethe data bandwidth available for communication between the probe deviceand the main unit. Additional channels also may permit interoperabilitywith multiple wireless systems and/or probes, for example, within acertain vicinity of the main unit. It should be appreciated that thecommunication channels may refer to communication in either direction;namely from the probe to the main unit and from the main unit to theprobe.

Robustness and dependability of the communication channel may befacilitated through a variety of methods and techniques. For example,channel redundancy may be used particularly in the presence ofinterference or noise. In some embodiments, this may be accomplished byswitching channels (e.g., automatically) when a channel is occupied byanother system, if an excessive or otherwise predetermined amount ofdata errors are detected, and/or if signal quality is deemed deficient.Another method of improving interoperability may include eachtransmitter (e.g., either in the probe or main unit) to automaticallyadjust its signal level depending on signal conditions perceived by thecorresponding receiver (e.g., either in the main unit or probe).Robustness also may be implemented in some embodiments by allowing thecommunication channel to operate in as wide a band as possible tominimize the effects of narrowband interference.

It should be appreciated that such functionality may be a part of theprimary communication channel and/or alternate or additionalcommunication channels. As such, the additional channels may be of thesame communication type as the primary channel. Alternatively, in someembodiments, the primary and additional channels may have somedistinguishing characteristics, like different operating frequencies,orthogonal characteristics (e.g., time, phase, and/or code divisionmultiplexed).

In just one example, in the wireless context, ultra wideband (UWB)techniques may be used for the communication channel to allow thecommunication channels to allow multiple data streams betweentransceivers in close proximity. At present, UWB permits data rates ofup to 1 Gbits/s for a single link. For example, an interface device thatmay be employed by some embodiments may include the WiQues™ chipset,part number WQST110/101. In some embodiments, a probe may have multipleparallel wireless channels running simultaneously using UWBcommunication methods. Also, it should be appreciated that multipleparallel communication channels may be included in some embodiments toprovide a greater data rate. In some embodiments, it may be desirable touse fewer communication channels to reduce physical size and powerrequired of the additional components needed to achieve additionalcommunication channels.

It should also be appreciated that in addition to the primary channelbeing the same or different than the alternate channel, the alternatechannels may be different from one another. For example, in someembodiments, some alternate channels may be based on infrared (JR)technology while the other alternate channels may be based on radiofrequency (RF) communication.

In some embodiments, using different or similar main and alternatechannels may permit communicating between certain devices, whilepreventing communication between other devices. Also, it should beappreciated that multiple receive devices on the probe and/or main unitand/or multiple communication channels may be employed. The multiplereceive devices may be located in certain locations on the devices toprovide a larger area of coverage.

Alternate communication channels may be set up such that one channel iswireless while another channel is wired. Also, some channels may bedigital and some channels may be dedicated to data (e.g., the same ordifferent data), while other channels may be dedicated to control data.The various channels may cooperate to increase a transfer rate of thedigital ultrasound data and/or to minimize a transfer of errors of thedigital ultrasound data. Certain channels may provide a greaterdirectional communication path than another communication channel and/orallow the main unit to initiate communication with the remote unit orvice versa. Also, one or more of the channels may communicate a uniqueidentifier with the data, where the unique identifier is used forinitiating communication with the remote unit, synchronizingcommunication with the remote unit, and ensuring communication with apredetermined remote unit. The type of data that is communicated on aparticular channel may be varied based upon a capability of the remoteunit, power status of the remote unit, capability of the main unit,power status of the main unit, frequency range, array configuration,power warnings, quality of transmission of the data, quantity of errorsin transmission of the data, availability of power of the main unit,availability of power of the remote unit, a change in transmission rate,and/or transmission characteristics of the data, etc.

In addition to employing multiple receivers, it should be appreciatedthat in some embodiments the main unit and/or probe may employ multipleantenna devices in communication with the receivers. For example, in theRF wireless context, the main unit may have more than one receiveantennae in order to use antenna diversity to combat multipath effectssuch as distortion and signal nulls. The multiple antennae and diversitymay help improve robustness by providing better signal coverage. Also,in some embodiments, the multiple antennae may be physically separatedfrom each other to reduce multipath propagation effects. In someembodiments, signals may be chosen based on amplitude, phase, SNR, etc.

Using a wireless probe or a wired probe using a relatively smaller cableto communicate, in some embodiments may dictate that additionalprocessing is performed within the probe device and/or outside of themain unit. The disclosed embodiments contemplate several techniques forallowing some processing to occur both within and outside of the probe.For example, in some embodiments, synthetic transmit focus techniquesmay be used. In some of those embodiments, synthetic transmit focus mayallow the received echo waves to be partially beamformed,non-beamformed, and/or some combination thereof.

Some embodiments may include a receive beamformer in the probe thatconducts partial or full beamforming. Also, some embodiments may includea transmit beamformer in the probe that conducts partial or fullbeamforming. These embodiments may be used in lieu of, or in combinationwith, the synthetic transmit focusing techniques.

Multibeam acquisition methods may be used in some embodiments to acquiredata in various scan directions, and/or a relatively large region of theimage frame. This may be accomplished in some embodiments substantiallysimultaneously. By requiring fewer transmit events, multibeamacquisition may provide increased acquisition of image frames. Someembodiments may decrease the rate at which image frames are acquired inorder to permit greater signal-to-noise-ratio (SNR) and/or improvedresolution, etc. by acquiring greater amounts of data per frame. Inother embodiments, an image frame may be acquired using multibeamacquisition using just one transmit event. Some embodiments may employtechniques other than multibeam acquisition, particularly where reduceddata bandwidth is desirable, and the embodiments contemplate suchalternatives.

In addition to providing techniques for allowing some processing tooccur within the probe, some embodiments may require to minimize suchprocessing and or corresponding components. For example, in someembodiments, it may be necessary to reduce the physical size of theprobe (e.g., size and/or weight) in order to permit easier use andmanipulation by the user. In addition, in those embodiments where theprobe includes its own source of power, like a battery, it may bedesirable to reduce the required size and weight of the battery forsimilar user dexterity reasons.

Notwithstanding these techniques, data bandwidth from the probe may beminimized in order to operate within the certain requirements ofwireless technology. Techniques that address this need include basebandsampling and matching the sample rate to the final display resolution.Other methods to better manage the data rate from a wireless probeinclude the use of a frame buffer within the probe and adaptivelymanaging the probe data rate in response to the available wirelessbandwidth. A proposed wireless interface is described with particularattention to features novel to the art of wireless ultrasound probes.Actual data rates are provided for a perspective on alternative systemdesigns.

In some embodiments, the nature of the wireless communication may bemodified based on various conditions. For example, an availablecommunication capacity of a particular remote, main or othercommunication unit may be monitored and the communication (wireless orwired) of the ultrasound data may be changed to another transmissionrate based on the available communication capacity. The rate may beincreased, decreased, and/or changed in some other way (e.g,transmission protocol technique, etc.). Also, a power level of one ofthe units may be used to adjust the data rate. For example, the rate maybe increased, decreased, and/or changed in some other way (e.g,transmission protocol technique, etc.) based on the power level. Thepower may be provided by a direct current (DC) source like a battery,for example.

Also, other unit performance characteristics may be changed as afunction of some operating characteristic of the probe and/or main unit,like the power level or power source and/or the temperature of the probeor main unit. The temperature of the probe may be determined by thermalsensors located proximate to a transducer in the probe and/or proximatea surface of a probe enclosure. These changes may be based uponperformance characteristics like an image quality provided by the probe,a drive voltage provided to a transducer in the probe, a voltagewaveform provided to the transducer in the probe, a quantity of elementused to transmit digital data representative of the ultrasound echowave, and an acquisition frame rate. The techniques also may provide forgiving an indication representative of the changes in the performancecharacteristics of the probe, main unit, and/or other device. Forexample, the indication may be a power saving mode light.

The user may change a power state of the probe from a low power state toa relatively more active power state by activating a portion of the userinterface, holding the probe, and/or simply moving the probe. Thesechanges in power state may include on to off, off to on, lower power tohigher power, and/or higher power to lower power, for example.

FIG. 9 is a flow diagram of a method 900 for establishing a link betweena probe and a main unit. It should be appreciated that although themethod includes just the probe and the main unit, the link may involveother components and processes. Also, the embodiments contemplate othermethods for establishing such a link.

The primary and/or alternate channels also may be used to sense aproximity of the main unit from the probe and vice versa. For example,in some embodiments, the primary and/or alternate channels may employIR, capacitive, inductive, magnetic, and/or any other technique commonlyused in sensing a proximity of one device from another.

Proximity sensing may be employed for a variety of purposes, all ofwhich are contemplated by the disclosed embodiments. For example, insome embodiments, it may be desirable to establish an exclusive linkbetween a particular probe and a particular main unit based on aproximity between the two and/or between other devices. Sincedetermining proximity may be difficult using signal properties of aprimary RF communication channel, for example, an alternate channel maybe utilized in order to facilitate the linkup process. Some alternatecommunication channels described above (e.g., IR) may be highlydirectional while others may be specifically designed for proximitysensing. These channels may be used alone and/or in conjunction withanother communication channel, for example, during the linkup process.

An exclusive link between probe and main unit may serve a variety ofpurposes including providing for interoperability of multiple wirelessprobe-based systems in close proximity to one another, for example. Thischaracteristic of the exclusive link, in some embodiments, may include atemporal limitation. For example, it may be desirable to allow theexclusive link to endure for at least one operating session and/or oversome predetermined period of time.

The exclusive link may be initiated by either the probe or the main unitor by some other means. For example, a user may press a button or thelike located on the probe, main unit or other device. The exclusive linkmay be established by communicating a particular data sequence and/orparticular data character between the main unit and the probe.

Also, the linkup process may allow the main unit and remote unit (oranother unit) to distinguish and/or identify each other. For example,the distinction may be accomplished by determining a proximity of themain unit to the remote units, a relative strength of a signalcommunicated by the main unit with the remote units, a predeterminedidentifier, and/or an absence of the another remote unit. Thepredetermined identifier may include a registered identifier and/or anidentifier used in a previous communication between the main unit andthe remote units. This also may be accomplished through the use ofcontrol data that is unique to the main unit and the remote unit, wherethe control data initiates, synchronizes and/or ensures communicationbetween the main unit and the remote unit. This communication may befacilitated by the use of one or more antennae located the main unit andthe remote unit. The antennae may be arranged to prevent multipatheffects including distortion and signal nulls.

In one embodiment, as shown in FIG. 9, for example, the probe mayinitiate communication with a nearby main unit by transmitting a “linkuprequest” command at 901 over the wireless communication channel, forexample. At 908, it is determined whether the main unit has received thelinkup request. If the main unit has not received the linkup request,the main unit continues at 908 to wait for the linkup request. If themain unit has received the linkup request, in some embodiments, the mainunit may respond with a “linkup acknowledge” command at 907 sent back tothe probe. This “linkup acknowledge” command may provide informationrelevant to the communication. For example, the “linkup acknowledge” mayindicate that the probe is within sufficient range of the main unit topermit wireless communication. Also, the proximity sensing and linkupcommunication may allow either the probe and/or main unit toautomatically wake up from a low-power state, standby mode, and/orotherwise change power status.

At 902, the probe determines whether is has received the linkupacknowledge. If the probe has not received the linkup acknowledge, themethod may return to 901 to wait for another linkup request. This returnmay occur after a predetermined condition, like a timeout or anotherpredetermined period of time.

If the probe has received the linkup acknowledge, in some embodiments,at 903 the probe may communicate back to the main unit with a “linkupconfirmation” command to indicate that the communication is established.At 906, the main unit may determine if it has received the linkupconfirmation. If the main unit has not received the linkup confirmationthe method may return to 907 to wait for another linkup acknowledge.This return may occur after a predetermined condition, like a timeout oranother predetermined period of time. If the main unit has received thelinkup confirmation, in some embodiments, at 905 the main unit maycommunicate back to the main unit with a “linkup complete” command toindicate that the linkup is complete. Along with the linkup completecommands the main unit may provide control commands to the probe. At904, the probe may loop to wait for the commands.

It should be appreciated that the linkup commands may be initiated byeither the probe, main unit, and/or some other device, and thus theparticular commands may be sent by any of the devices. Also, it shouldbe appreciated that additional communication and corresponding commandsrelevant to the linkup of the devices are contemplated by the disclosedembodiments. In addition, the linkup may be attempted a certain numberof predefined times before it is ceased.

In order to facilitate the linkup process, in some embodiments, both theprobe and main unit may be pre-assigned unique identifier codes oridentification numbers (e.g., serial numbers), that may be communicatedbetween the main unit and probe (and perhaps other devices) during thelinkup process.

The identifier codes may allow, for example, subsequent exclusivity withrespect to further communications between the probe and main unit andallow interoperability with multiple wireless probe-based systems inclose proximity. It should be appreciated that in some embodiments,interoperability may be a consideration during the linkup process. Forexample, interoperability and exclusivity may be appropriate where thereare multiple main units and/or probes or the like within the wirelesscommunication range that may respond to the probe's and/or main unit'srequest. In some embodiments, it may be desirable to permit the probeand/or main unit that are in closest proximity to one another to linkup,while in other embodiments it may be appropriate to use other metrics(e.g., signal strength, power status and availability, use selection,most recently linked, etc.).

It should be appreciated that other techniques for accomplishingdiscrimination between the probe, main unit and/or other devices arecontemplated within the disclosed embodiments. For example, non-wirelessor wired communication techniques may be used in some embodiments. Thetechniques may include making electrical and/or magnetic contact betweenthe probe and main unit and/or by allowing a user to press a button onthe main unit.

It should be appreciated that the linkup process may be automatic ormanual, or a combination of both. For example, some embodiments maypermit the entire linkup process to occur without requiring the probe,operator or other device to make contact with the main unit. Otherembodiments may require the user to initiate certain portions of theprocess manually. For example, the user may select a probe type from adisplayed list of available probes resulting in the main unit sending alinkup request to probes of the selected type.

In some embodiments, it may be that after the linkup process has beencompleted, the probe and main unit may include some information (e.g.,their identification numbers) in some or all subsequent communication.This may permit the devices to avoid subsequent conflicts ormiscommunication with nearby systems. In addition, the probe and mainunit may store their own and each other's identification numbers inorder to facilitate subsequent linkups after a particular session isterminated or placed in a non-operative mode. For example, theidentification numbers may be stored temporarily or permanently innon-volatile memory such as EEPROM, Flash PROM, or battery powered SRAM,well known to those skilled in the art. In this way, if the link betweenthe probe and main unit link is terminated or discontinued for someperiod, either device (or another device) may attempt to reestablish thelink. Such attempted reestablishment of the link may be accomplishedautomatically (e.g., periodically), upon some operator action, or basedon some other input.

As shown in FIG. 2, the main unit may include or be in communicationwith a display unit. The display unit may display information about themain unit, a linked or other probe, and/or another device. With regardto the probe, the display may provide details regarding the probe type(e.g., frequency range, array configuration, etc.), an identifier codeor number, a user pre-assigned name, etc. The name of the probe may bedetermined by the user and entered at the main unit, communicated to theprobe, and written into non-volatile memory within the probe for futurereference. Alternatively, it may be entered directed into the probe andcommunicated back to the main unit. The display also may showinformation relating to the probe's battery charge status, such as theamount of time the device has left of battery power. Such informationmay be relevant in some embodiments, for example, where an operator oruser may be about to initiate an ultrasound exam and may need to changebatteries before beginning the exam. The display also may providelow-battery warnings when the battery reaches a predetermined depletedstate, for example. Also, the display may indicate any other operationalerrors with the system (i.e., main unit, probe, and/or other devices)during a diagnostic or self-test.

Instead of, or in addition to, providing a display indication related tothe probe, some embodiments may have indications (e.g., LEDs) on theprobe housing, main unit and/or other device. In some embodiments, itmay not be desirable to have such indicators on the probe device becauseof the extra power drain on the battery that may result. In someembodiments, it may be desirable to provide detailed charge stateinformation to the main unit at all levels of charge so the user canmonitor and take appropriate action before the battery is depleted ornearly so. In these embodiments, by displaying a charge state on themain unit display instead of the probe device, there may be noadditional battery discharge in the probe. Also, the display may permita user to continuously or nearly so view the charge state duringimaging, while still being able to view the remainder of the relevantinformation without interruption.

Power may be provided to the main unit, probe and other devices using avariety of techniques. For example, the main unit may operate onalternating current (AC) power, battery power or other alternative powersources. Similarly, the probe may operate on alternating current (AC)power, battery power or other alternative power sources. In theembodiments where the probe is wireless or thin-wire, or otherwiseincapable of receiving power from an AC source for some period of time,it may be that the probe receives power from a battery, solar power, orother non-AC power source. Although the remainder of the disclosure mayrefer to battery power generally, it should be appreciated that suchreferences include other power sources including, at least partially, ACpower, solar power, and fuel cell sources. Because of the medicallysensitive nature of the probe, it may be desirable to ensure that suchbattery power is available at all times. For example, a backup batterypower source may be necessary in some embodiments.

In some embodiments, it may be desirable to conserve available probepower. Such conservation of energy may be limited to a certain period oftime, in some embodiments. This may be accomplished using a variety oftechniques contemplated by the disclosed embodiments. For example, theprobe's circuitry may be turned off or powered down under certainpredetermined conditions, like when such circuitry is deemedunnecessary, for example.

In some embodiments, the system may adapt to a change in battery chargeby altering acquisition parameters and/or other system operatingconditions. Such changing acquisition parameters may trade off imagequality or frame rate for power usage, for example. For example, suchchanging acquisition parameters may include reducing the number ofactive receiver channels in the probe to reduce receiver powerconsumption. Reducing acquisition frame rate or transmit voltage mayalso lower power consumption, and hence, conserve battery power. Someembodiments may alert the user to changes in operating conditions causedby changes in battery charge state. For example, a message appearing onthe system display may indicate a power saving mode level.

Similarly, in some embodiments, the system may adapt to the status of anoptional thermal sensor located at the probe face by adjusting varioussystem operating conditions to trade off image quality for lowertransducer heat generation. Example parameters include the transducerdrive voltage level, drive waveform, number of active transmitterelements, acquisition frame rate, etc.

In some embodiments, the main unit may operate on battery power, orperhaps also conserve electrical power usage. Therefore, like the probe,a main unit low-power state, a “standby” or “sleep” mode may beactivated after some period of inactivity. The period of inactivity maybe terminated automatically, by manual intervention, or some combinationthereof. For example, in some embodiments a user may simply change thepower status of the probe and/or main unit by pressing a button, ormerely handling the probe via motion sensing (e.g., using anaccelerometer and/or tilt switch, etc.). Also, the power status of theprobe and/or main unit may be changed by the probe sensing a grip of theuser's hand (e.g., by detecting heat, capacitance change, pressure,etc.). In some embodiments, it may be desirable to use a combination ofsensing methods and/or to allow activation by deliberate operator actionso it may not be triggered accidentally.

Other methods for conserving and controlling power status of thecomponents in the system may include manual and/or automatic changing ofpower conditions (e.g., power off) to the components once a procedure iscompleted. The termination and/or changing of power conditions may bebased on some predetermined period of time accrued by a timer in thesystem. For example, if a component like the probe is not operated forsome period of time, the component may change its power state (e.g.,turn itself off and/or place itself into a different power state). Adifferent power state may include a relatively lower or higher powerstate. In some embodiments, this may be accomplished by changing thepower state of a certain number of the portions of the probe or otherdevice. For example, when imaging is in a “frozen” state (i.e., no liveimaging) the probe's data acquisition and/or wireless interfacetransmitter circuitry may be turned off.

Initiating the change in power state may be accomplished in a number ofways all of which are contemplated by the disclosed embodiments. Forexample, some embodiments may contemplate various techniques fordetecting a lack of activity, including the probe using motion,acceleration, heat and/or capacitance, or the like. Also, someembodiments may measure inactivity dictated by a period of time wherecontrols on the probe, main unit, and/or other device are not operated.Also, following such inactivity, the component could power down eitherimmediately and/or after some delay. The time period could be specifiedby the user and/or by some component in the system, including the probe,main unit or other device. Because in some embodiments, the main unitmay communicate control information (e.g., periodically) to the probe,it may be desirable to allow the probe to detect a lack of controlcommands (e.g., over an extended period of time) from the main unit. Forexample, the probe may power itself down for a variety of reasonsincluding because the main unit is either no longer turned on, isinoperable, and/or has been moved to a location out of wirelesscommunication range, etc.

FIG. 10 provides just one example of a flow diagram 1000 for a probeinactivity timeout. As shown in FIG. 10, it is determined at 1001whether an activation control has been activated. If, at 1001, it isdetermined that an activation control has not been activated, a loopwill continue to check to see if an activation control has beenactivated. If, on the other hand, at 1001 an activation control has beenactivated, power is provided to the probe at 1002. At 1003, a timer isreset. The timer may be used to count to a predetermined time todetermine if the probe has been inactive long enough to turn off theprobe.

At 1004, it is determined whether a command is received by the probe,for example, from a main unit and/or another device. If, at 1004, acommand is received by the probe, the timer is reset at 1003. If, on theother hand, at 1004, it is determined that a command is not received bythe probe, it is determined at 1005 whether activation control isreceived by the probe. If, at 1005, it is determined that activationcontrol is not received by the probe, the timer is reset at 1003. If, onthe other hand, at 1005, it is determined that activation control isreceived by the probe, it is determined at 1005 whether a timeout hasoccurred. If, at 1005, it is determined at 1005 that a timeout hasoccurred, the probe is powered off at 1008. If, on the other hand, at1005, it is determined at 1005 that a timeout has not occurred, at 1007,it is determined whether the timeout almost has occurred. If, at 1007,the timeout almost has occurred, the main unit may be informed of theimpending timeout at 1009. If, on the other hand, at 1007, it isdetermined that the timeout almost has not occurred, the timer is resetat 1003.

In some embodiments, it may be desirable to permit the probe to remainactive for some predefined time period after initial linkup, forexample. It may be such that when the predefined period of time is aboutto run out, some indicator may be displayed for the user either on theprobe (e.g., via a LED), the main unit (e.g., via a display), and/orboth.

In addition, it should be appreciated that in some embodiments, the mainunit and other devices may include similar non-AC power concerns andcapabilities described above with regard to the probe.

In addition to providing and controlling power, some embodiments mayinclude monitoring a charge or other status of the battery while in useand/or dormant. For example, in some embodiments, a controller maymonitor the battery. The controller may be a separate part of the systemand/or built into the battery pack. In some embodiments, the controllermay track the characteristics of the battery and its use. For example,the controller may keep track of the amount of time the battery has beenused, as well as the charge and discharge cycles. Also, the controllermay provide feedback to the system and display such information to theuser regarding the battery's current charge state. This may beaccomplished, for example, by monitoring such parameters as thebattery's open-circuit voltage, integrated current in and out since lastfull charge, etc. In some embodiments, such information may betransferred between the battery and probe or other devices usingcommunication channels. Also, in some embodiments, estimating batterycharge state may be accomplished using battery open-circuit voltage,load current integration over time (e.g., coulomb counting), and/orbattery source resistance, for example.

In this way, the controller may facilitate real-time understanding ofthe battery's capability as well as predict future performance of thebattery.

It also should be appreciated that the battery interface may includesome physical characteristics specific to medical environments. Forexample, the battery interface may need to be tolerant and/or resistiveof gel and/or other conductive liquids.

FIG. 11 is a diagram of an example battery monitoring and controlcircuit 1 100 that may be used to monitor and/or control a battery foruse with a probe 1105. In some embodiments, the battery may be arechargeable type of battery for example, a Lithium ion battery. Anover-voltage (OV) diode 1102 may be used to protect internal circuitryfrom electrostatic discharge (ESD) events. Also, a flip-flop device 1103may be used to store a current on-off state, and may be connected to anON/OFF switch 1104. Switch 1104 also may have other additionalfunctionality, for example, after probe 1105 is operating.

To activate probe 1105, a user may press switch 1104, for example, bydepressing it for a certain period of time (e.g., 100 mS or more). Toturn probe 1105 off, a microcontroller 1106 may monitor switch 1104 todetermine whether it has been depressed for a certain period of time,for example, 3 seconds or more. In some embodiments, after switch 1104is released after being depressed for a predetermined period of time,microcontroller 1106 may send a battery monitor shutdown command. Thecommand may provide a rising edge on a clock input of flip-flop device1103, and operate to turn off probe 1105.

When flip-flop device 1103 is in a reset state, transistor 1107 isturned on, and power is connected to battery monitor and user interfacecontroller (BMUIC) 1108. In some embodiments, BMUIC 1108 may be amicrocontroller with analog/digital inputs, two op-amps and atemperature sensor. Once power is provided to BMUIC 1108, it may begingathering data about battery 1101. For example, if battery 1101 hassufficient capacity, BMUIC 1108 may provide power to the remainder ofprobe 1105. BMUIC 1108 may have control of power provided to theremainder of probe 1105 by driving transistors 1109 and 1110. BMUIC 1108also may power itself down in some embodiments, for example, if battery1101 has a reduced charge to some degree, and/or if probe 1105 is turnedoff by the user and/or by command from the main unit or some otherdevice.

Output of op-amp 1111, available at A/D input 2 of microcontroller 1106may measure current drawn by probe 1105. Full scale range of the currentload sensor may be approximately 2 amps. Average current load of probe1105 in operation may be 0.5-1.0 amps. Once probe 1105 is running,source resistance of battery 1101 may be monitored continuously bymicrocontroller 1106. The load current of probe 1105 may vary, forexample, depending on the operating mode, and by monitoring load currentand terminal voltage of battery 1101. Source resistance of battery 1101may be calculated as a change in the battery terminal voltage divided bya change in load current. Knowing resistance, current load and terminalvoltage of battery 1101, for example, it may be possible to calculate avirtual open-circuit voltage of battery 1101.

Also, available to microcontroller 1106 may be the temperature of probe1105 housing. A temperature sensor 1112 may be located near battery1101, and may be used to sense ambient temperature. As is well known tothose skilled in the art, battery temperature may have a relativelysignificant effect on its capacity. In some embodiments, for example, inhospital and clinical environments, normal conditions will have ambienttemperatures of approximately 20-30° C. In some embodiments, battery1101 may have a charge reserve of about lampere-hour, so that a fullycharged battery may supply approximately an hour of operational time.Typically, within a relatively short period of time after being attachedto probe 1105, battery 1101 may be fairly close to the ambienttemperature, even if it started out at a significantly differenttemperature. Therefore, in some embodiments, sensing of the temperatureof battery 1101 may not have a relatively large effect on the overallcircuit accuracy.

Measurements of current consumption, battery terminal voltage andambient temperature, for example, may be communicated through a wiredand/or wireless interface back to the main unit and/or some otherdevice. Estimate of the remaining battery capacity may be made at themain unit, probe 1105, and/or some other device. In some embodimentswhere determination is made at a place other than probe 1105, thecomplexity of the algorithm used to estimate the remaining capacity inbattery 1101 may not be constrained by the likely reduced processingcapacity of microcontroller 1106.

The main unit may display on the main imaging display screen an estimateof the remaining battery capacity based on current and expected probeusage patterns. In some embodiments, such usage data may not beavailable to microcontroller 1106, and so it may be desirable toimplement a battery capacity estimation algorithm in the main unit.

BMUIC 1108 also may implement numerous safety features. For example,BMUIC 1108 may allow probe 1105 to discharge the battery only to acertain predetermined level, after which it may terminate operation.Also, in some embodiments, BMUIC 1108 may provide over-currentprotection for probe 1105, and perhaps terminate probe operation toprotect the probe and battery pack. In some embodiments, thresholds forthese values may have default values and/or also may be modifiable bythe main unit, for example, as probe commands.

It should be appreciated that in some embodiments, measurements ofbattery terminal voltage, current consumption, temperature and estimatedbattery source resistance and open-circuit voltage may be sent back tothe main unit through a wired and/or wireless link. These values may becommunicated at various intervals, for example, every 10-30 seconds.

BMUIC 1108 also may act as a user interface controller for probe 1105.It may receive switch inputs, potentiometer settings, pointing deviceinputs, etc. from user interface input devices 1113, and supply thesecontrols to the main unit through a wired and/or wireless interface. Theuser interface may include a number of features that allow a user tointeract with probe 1105. For example, the user interface may include adepressable button, a motion detector, an acceleration detector, a heatdetector, and a microphone. Also, the user interface may provide anindication to the user of a number of things. For example, although notexclusive, the user interface may provide power status, designation ofremote unit, type of remote unit, frequency range, array configuration,power warnings, capability of the remote unit, quality of transmissionof digital data, quantity of errors in transmission of digital data,availability of power required for transmission of digital data, changein transmission rate, completion of transmission, quality of datatransmission, transmission characteristics of the non-beamformedultrasound wave, processing characteristics of the echoed ultrasoundwave, processing characteristics of the digital data, and transmissioncharacteristics of the digital data, etc.

BMUIC 1108 also may receive display data from the main unit and/or otherdevice and present it on user interface display 1114. It should beappreciated that microcontroller 1106 may provide additional operationalfunctions for other subsystems within probe 1105.

FIG. 12 is a flow diagram 1200 of a power control technique that may beimplemented by BMUIC 1108. It should be appreciated that the disclosedembodiments contemplate a number of power control techniques. Forexample, the disclosed embodiments may include a power controller thatcontrols the power the power source and adjusts the electrical energyfrom the power source. Such control may be accomplished by changing aload, like the transducer and the transceiver, for example. Also, thepower controller may adjust the electrical energy from the power sourcebased an amount of the ultrasound data communicated by the transceiver.Similarly, the transceiver may adjust communication of the ultrasounddata based on a characteristic of the power source, like capacity, type,charge state, power state, and age of power source. The power source maybe a direct current source, like a battery. The power control techniquesmay also increase, interrupt, and/or reduce power from the power sourcedepending upon time immediate or after a certain amount of time, like aduration from an initial application of the electrical energy, apredetermined threshold of available electrical energy, a predeterminedamount of time, and a predetermined amount of inactivity. The inactivitymay include a user pressing a button, a motion detector locatedsomewhere within the system, an acceleration detector, a heat detector,and a microphone (e.g., for voice-activated commands).

It should be appreciated that the power controller may adjust theelectrical energy provided any of the components of the system includingthe transducer, analog-to-digital converter and transceiver, etc. Acommand to power down any of these components may be received from aprobe, a remote unit, the main unit, or another unit.

As shown in FIG. 12, when the ON/OFF button is pushed in 1201, flip-flop1103 will reset, turning on transistor 1107 and supplying power to BMUIC1108 in 1202. BMUIC 1108 powers up and waits at 1203, for example for100 mS. The waiting period may allow the power supply to settle andstabilize, and/or provide a “debouncing” delay for the ON/OFF switch. In1204, BMUIC 1108 measures battery terminal voltage and ambienttemperature and makes an estimate of the remaining capacity. If thecapacity is not above the minimum capacity threshold, probe 1105 may beturned off at 1201. If, on the other hand, it is determined at 1205 thatthe capacity of the battery is above the minimum capacity threshold, at1206, it is determined whether the on/off button is still depressed. Ifit determined at 1206 that the button is not depressed, probe 1105 maybe turned off at 1201. If, on the other hand, at 1206, it is determinedthat the on/off button is still depressed, BMUIC 1108 may issue a “probeon” command that drives transistors 1109 and 1110 and supplies power tothe remainder of probe 1105 to run the probe at 1207.

While probe 1105 is running, BMUIC 1108 monitors user interface inputs1113 to determine whether new inputs are being provided, at 1208. If, at1208, it is determined that new user inputs are being received, the newuser inputs may be sent to the main unit and/or another device at 1209.The data may be communicated via a wired and/or wireless interface. If,on the other hand, at 1208 it is determined that no new user inputs arebeing received, it may be determined at 1210 whether any additional dataand/or information from the probe or another device needs to bedisplayed by BMUIC 1108 on the user interface display. If, at 1210, itis determined that such new data and/or information should be displayed,the user interface display may be updated at 1211. For example, in someembodiments, user interface inputs may be “soft keys” whose functiondepends on the current operational state of probe 1105. Such soft keylabels may be displayed on the user interface display to convey theirfunction. In some embodiments, this labeling information may bemaintained locally in BMUIC 1108 and provided to the display. Also,there may be special diagnostic modes of operation wherein internal dataand measurements within probe 1105 may be displayed on the userinterface display. It should be appreciated that other types of dataand/or information may be updated.

If, at 1212, it is determined that a power off command has not beenreceived from the main unit and/or another device, the control datacommands may be executed at 1213. If, at 1212, it is determined that thepower off command has been received from the main unit and/or anotherdevice, probe 1105 may be turned off at 1201. After the commands havebeen executed at 1213, it may be determined whether the on/off buttonhas been depressed for a predetermined period of time. If, at 1213, itis determined that the on/off button has not been depressed for apredetermined period of time, process 1200 will return to 1208. If, onthe other hand, at 1213, it is determined that the on/off button hasbeen depressed for a predetermined period of time, probe 1105 may beturned off at 1201.

In some embodiments, particularly those perhaps involving a wirelessprobe for example, it may be that certain interfaces may be created tomaintain a sterile environment. For example, some embodiments may createa user interface that permits operation of the system with little or noneed to access portions of the system beyond the sterile boundary. Inthe context of a user interface to the probe, some embodiments may keepan operator from having to manually reach out beyond the sterile fieldto change system settings or make adjustments. Instead, such embodimentsmay permit the user to make such adjustments and control the system fromthe probe housing that may be located within the sterile field. In thoseembodiments where the probe is located within a sterile sheath, theinterface may remain operable. In order to facilitate such sterility,some embodiments may provide a control interface on the probe. Thecontrol interface may include a touch pad, an LCD touch screen withsoft-keys, another pointing device, etc.

Also, “hands-free” operation of the system may be facilitated byallowing voice-based commands to be processed by the system via amicrophone. The microphone may, for example, be built into the probe,the main unit, and/or any other parts of the system to allow a user tocontrol the system with voice commands. In some embodiments,particularly where the microphone is installed on the wireless probe,the voice-based command may be converted and communicated over a wiredor wireless link with the main unit and/or other system component.

In some embodiments, the wired or wireless link may be the same as, ordistinct from, the link over which the ultrasound data is communicatedin the system. For example, image acquisition data, control data andmicrophone data may be packetized and sent to the main unit over thewired or wireless interface. In some embodiments, where more than onedata stream is sent across the same communication channel, the datastreams may be multiplexed. It should also be appreciated that if thewired or wireless channel cannot handle the amount of data, one or moreof the data sources may be adaptively altered to accommodate theavailable bandwidth. For example, the microphone signal sampling rateand/or dynamic range may be scaled down if the wireless communicationlink is not large enough.

FIG. 13 is a block diagram illustrating data merger and adaptive controlsystem 1300. As shown in FIG. 13, a microphone 1301 is in communicationwith an amplifier 1302. Amplifier 1302 is in communication with ananalog-to-digital (A/D) converter 1303. A/D converter 1303 may operateto sample and digitize a signal from microphone 1301. A/D converter 1303may have a sampling rate that may be adjusted by an adaptive controlinterface 1312 that may be responsive to a controller within the probe,the main unit, and/or another device. A microphone packetizer 1304 incommunication with A/D converter 1303 may provide an adjustable numberof bits per sample and/or dynamic range of the microphone signal data.Microphone packetizer 1304 also may encode the data in a compressedformat using any number of standard and/or proprietary audio compressiontechniques (e.g., MP3) for further data reduction and possibly withvariable compression parameters responsive to the adaptive controlinterface 1312. Microphone packetizer 1304 also may arrange themicrophone audio data into discrete packets before merging with otherdata sources via a data merger 1310.

Also, as shown in FIG. 13, an outgoing control packetizer 1309 mayreceive control inputs from pushbuttons, knobs, trackballs, etc. and mayarrange the associated control data into discrete packets before mergingwith other data sources via data merger 1310. Image data also may bepacketized via an image data packetizer 1307 before data merger 1310.Image data packetizer may receive an image via transducer 1305 and imageacquisition 1306. Battery status information may be generated by batterymonitor and power controller 1308 function and passed to data merger1310 to merge with other data sources. A thermal sensor (e.g., athermistor) may be located where the probe makes contact with the bodyin order to sense probe temperature at the patient interface. Thethermal sensing functionality may translate a signal from the thermalsensor into thermal status information to be sent to the main unit, forexample, via data merger 1310. Both the battery and thermal statusinformation may be made available in discrete data packets. Data merger1310 may prioritize multiple data sources according to a predeterminedand/or adaptively adjusted priority level. Data merger 1310 also maymerge the data packets into one or more data streams leading to thewired and/or wireless interface 1311.

It should be appreciated that this description encompasses many types ofprobe designs including non-invasive, external probes as well assemi-invasive and/or invasive probes such as percutaneous,catheter-based, endo-cavitary, transesophageal, and/or laparoscopicprobes in wired and/or wireless embodiments. For example, certaincatheter-based, endo-cavitary, transesophageal, and/or laparoscopicprobes are contemplated as wired and/or wireless probes.

Catheter-based ultrasound transducer probes may be used forintra-luminal and intra-cardiac ultrasonic imaging. There are varioustypes contemplated by the disclosed embodiments including rotatingsingle element, radial array and linear phased array. Rotating singleelement probes may be simpler to manufacture but may provide relativelypoorer images due to their fixed focal depth. Also, in some embodiments,the scan plane rotating single element probes may be diametral to thecatheter shaft. Linear arrays may be oriented along an axis of the shaftof the catheter, and therefore provide an image in a plane that islongitudinal to the catheter shaft. Linear arrays are typically moreuseful on larger vessels because they generally require a largercatheter shaft. Matrix and/or two-dimensional catheter-based transducersare also contemplated. In addition to side-fire methods, these mayemploy end-fire array geometries As is the case with other types ofprobes, in some embodiments, sterility may be desirable for catheterprobes. As a result, embodiments that include a wireless catheter probefacilitate greater sterility by reducing and/or eliminating a need for awired connection to the main unit.

In some embodiments, the probe or other components may be able to beconfigured, programmed and/or calibrated over the wired and/or wirelesslink from the main unit or other component. For example, in someembodiments, when the probe powers up for the first time, it may be thatthe wireless link and its support circuitry are fully functioning. Theprobe may include support circuitry that may be a field-programmablegate array (FPGA) with a boot FEPROM. The FPGA may be an Altera Cyclone™FPGA or the like, that are provided with configuration data orcalibration data. In some embodiments, the FPGA may be programmed fromthe wired or wireless interface without the need for a boot EEPROM.Alternatively, the boot EEPROM may be reprogrammable via the wirelessinterface to facilitate firmware updates. In this case, the FPGA may beinitially programmed with the current FEPROM contents upon power up,after which time new programing code is loaded into the EEPROM from thewireless interface. The next time the probe is powered up, the FPGA maybe loaded with the new EEPROM contents.

In some embodiments, other components like an acquisition controller,signal processing blocks and probe identification circuitry may beprogrammed after power up. After establishing the wireless link betweenthe probe, main unit, and/or other components, an FPGA programmingcommand may be communicated over the link to program the acquisitioncontroller and the signal processing blocks. These blocks may also bereprogrammed to support different user input controls modes (i.e., colorvs. b-mode, etc.) and/or reprogrammed to optimize for different tissuetypes and/or various other operating conditions. Reprogramming may occurwhile the image is frozen, on a frame-by-frame basis, and/or before eachtransmit event if necessary.

In some embodiments, a control interface for an FPGA may include controllines along with one or more data lines. Alternatively, if any of thehardware in the probe is a microcontroller, software could be downloadedin a manner similar to that described for the FPGA. Configuration tablesfor acquisition timing and coefficients for filtering and other signalprocessing functions may be loaded over the link. These configurationsmay be different for various user-controlled settings such as depthchanges and/or mode changes, for example.

Configuration data or information may be provided from any of thecomponents in the system Such configuration data, may include withoutlimitation, power status, designation of device, type of device,frequency range, array configuration, power warnings, capability of aremote unit, quality of transmission of digital data, quantity of errorsin transmission of digital data, availability of power required fortransmission of digital data, change in transmission rate, completion oftransmission, quality of data transmission, look-up tables, programmingcode for field programmable gate arrays and microcontrollers,transmission characteristics of the non-beamformed ultrasound wave,processing characteristics of the echoed ultrasound wave, processingcharacteristics of the digital data, and transmission characteristics ofthe digital data, etc.

Probe identification like serial number, probe type, bandwidth, revisionnumber, and calibration data, for example, may be programmed intonon-volatile memory either over the wireless link or a wired programmingport. With respect to calibration, a calibration feedback loop may beinitiated where acquired data is transmitted to the main unit to performcalculations. The main unit may then communicate such information asoffset and gain data back to the probe where the data may be stored in amemory. In some embodiments, calibration may occur periodically and/oronly once during probe production. In the latter case, the storagememory device may be non-volatile such as flash memory or EEPROM.

In some embodiments, it may be desirable to allow the user to locate aprobe. For example, it may be that the probe is misplaced or the userneeds to select one of many available probes and needs the proper probeto be distinguished for the operator. The system may include locatorfunctionality that operates in a variety of ways contemplated by thedisclosed embodiments. For example, some embodiments may include locatorfunctionality with limited detection or geographic range, such thatprobes within the predetermined range (e.g., 10 meters) may be detected,while probes outside the range may be ignored in some embodiments. Also,the locators may have different characteristics, which may includeactive, passive or hybrid locator functionality, and the like.

Active locator functionality, for example, may include a receiver thatmay be of low power. The receiver would monitor (e.g., constantly,intermittently, etc.) for a particular electronic signature of theprobe. For example, the electronic signatures may include RF emissioncharacteristics, identification number, magnetic field signatures (e.g.,magnetic field of circuitry, magnetic fields modulated with a particularsignature, etc.).

In some embodiments, the probe may be identified to the user by a numberof audible or visible techniques. For example, the system may emit anidentifiable audible response, such as a beep for example, when itdetects the proper probe (e.g., receives a particular RF signature). Insome embodiments, the system may provide a visual indication, like theflashing of an indicator light when it detects the proper probe.Alternatively or in addition, it should be appreciated that theseindicators may work by indicating an improper probe to prevent the userfrom selecting and using the wrong probe. It should also be appreciatedthat other techniques for providing indication of and locating forprobes are contemplated by the disclosed embodiments. Also, in someembodiments, the indicators may be able to indicate a direction and/ordistance that the user may travel to find the probe. For example, theindicator and locator functionality may use global positioningtechniques, well known to those skilled in the art.

The communication between the locator components (e.g., receiver) may bethe same wireless and/or wired channel used to communicate the imageand/or control information between the probe, main system and otherdevices. Also, in some embodiments the locator functionality may havethe option to use alternate communication channels.

Some embodiments may allow the locator communication channel to operateusing techniques that allow reduced power consumption. For example, thelocator's receiver may be powered for relatively shorter periods of timeas needed, and then powered off when not needed (e.g., when waiting orafter probe has been located).

Passive locator functionality also is contemplated by the disclosedembodiments. These passive techniques may not require active or poweredcircuitry in the probe, or other devices. This embodiment may bedesirable where conservation of power in the system is a consideration.In this embodiment, for example, the locator functionality andcomponents may produce an identifiable signature when placed intoelectrical and/or magnetic presence of an external source (e.g., an RFfield).

In some embodiments, the external source may be attached to or housed inthe main unit of the system and/or other systems or non-system devices.Also, the external source may be removable from being anchored to thesystem so as to facilitate searching for a lost probe. The externalsource may be AC powered or battery operated for greater portability. Insome embodiments, the external source may emit a signal (e.g., a RFbeacon signal). Some embodiments may use a signal having a particularfrequency that is responsive with the passive receiver. As with theactive locator functionality, upon detecting and/or locating the probe,an indication may be made to the user. Some embodiments may include thelocator functionality within the probes such that one probe could beused to find another probe and/or to locate or distinguish itself, forexample. For example, it may be able to ignore itself and find anotherprobe by disabling the locator functionality while the probe is helpingto find another probe.

It should also be appreciated that a combination of the passive andactive techniques may be used in a hybrid system. For example, someembodiments may include a passive circuit sensitive to a particular RFsignature that generates a trigger signal to activate a remainder of thelocator components so that the probe can identify itself as described.

In some embodiments, the locator functionality may use relativelylow-frequency RF, and magnetic coupling to communicate. In this way, thelocator functionality may be able to operate over greater environmentalcircumstances and conditions. For example, using the low frequency,allows the generated magnetic fields to travel through more materialslike conductive enclosures. In this way, the probe may be located evenif it is placed in a metal cabinet, trash can and/or patient. Also, someembodiments may eliminate conditions like multi-path nulling by allowingthe coupling between the antennae and devices to create a near-fieldphenomenon. In this way, the signal strength may be more accuratelycalculated as a function of distance and allow the locator functionalityto be set to a power level that reliably covers a desired findingdistance, yet not so far as to stimulate probes at a greater distance.

In some embodiments, because of the relatively lower frequency, therequired power of the locator circuit may be reduced. For example, thepower level may be nominal as compared to battery capacity. In this way,in some embodiments, the locator functionality may be run continuously(or nearly so) as may be necessary to find a lost probe, yet userelatively little battery power.

FIG. 14 is a block diagram of a circuit 1400 that provides locatorfunctionality. Although FIG. 14 is an example of a specific circuit, itshould be appreciated that this is just one example of such a circuitand does not preclude the use of other components in the circuit or evenother circuits. The components shown and discussed may not represent allof the components that may be used, but are limited for the purposes ofclarity and brevity.

The probe locator circuitry may allow a probe to find a main unit, amain unit to find a probe, and/or a main unit and probe to find anotherunit, or vice versa. The locator functionality may be a part of a modulethat is located within the main unit, the probe, and/or another unit.The module may use global positioning, triangulation, radio frequencyidentification, and/or ultrawideband communication, for example.Communication for the locator functionality may be accomplishedwirelessly and/or over a wire. The locator may work independently ofand/or in conjunction with a proximity sensor using optical, infrared,capacitive, inductive, electrically conductive, and/or radio frequencytechniques. The locator functionality may be initiated by a user thatinteracts with the user interface, such as a momentary switch that theuser depresses continuously (or nearly so) to activate the locatorfunctionality.

The locator functionality may operate by providing an audible and/orvisible signal module that emits a sound or shows when the locatormodule identifies the remote unit, the main unit, and/or another unit.Of course, the indications also may be used to identify an improperremote unit, main unit, and/or other unit, and to prevents a user fromselecting the improper unit. The locator module may be designed, in someembodiments, to identify a location of the unit when the unit is within10 meters. Also, in some embodiments, perhaps to conserve resources likepower, the locator functionality may attempt to identify the location ofthe remote unit intermittently. Also, the locator functionality mayprovides an indication of a direction and distance that a user shouldtravel to precisely locate the unit and/or units. Also, the locatorfunctionality may passively produces a locator signal such that whenplaced into an electrical field and/or magnetic field, a signal isgenerated. The magnetic field may operate with a relatively lowfrequency to permit the magnetic field to travel through obstructions(e.g., trash can, file cabinet, etc.) to the locator module.

As shown in FIG. 14, an antenna 1401 may be constructed with an openmagnetic path. For example, the magnetic path may be an air coil with alarge radius and/or a solenoid having a high permeability ferrite rod.In some embodiments, the open magnetic path may permit magnetic fieldsto couple through the windings of antenna 1401. The magnetic field maybe created with a particular frequency, for example, centered at 8192Hz. Also, the magnetic field may have a certain spatial orientation, forexample, such that the magnetic flux path is substantially parallel tothe central axis of antenna 1401. In some embodiments, a tuned circuitwith inductor 1401 and capacitor 1402 may resonate with the impingingmagnetic field.

In some embodiments, a mixer transistor 1404 may be used and may beswitched on and off at a magnetic field frequency (e.g., 8192 Hz) thatmay include some mixing functionality to demodulate 8192 Hz to a DClevel of 0 Hz. For some embodiments, any modulation on the magneticfield may be translated in frequency by 8192 Hz. Amplifiers 1405 and1406, and their associated components, may comprise an intermediatefrequency (IF) amplifier and bandpass filter with a predetermined centerfrequency (e.g., 20 Hz). In this way, the IF amplifier output mayrespond to any double-sideband or single-sideband modulation that isapproximately at the center frequency from the carrier (e.g., 8212 Hz or8172 Hz). Also, the output of the IF amplifier may be AC coupled totransistor 1407 to operate as a simple voltage threshold comparator andrectifier. In some embodiments, for example when there is 20 Hzmodulation on the 8192 Hz carrier, and the received signal is ofsufficient amplitude, transistor 1407 may pull its collector low andhold it there while the signal is present. This may be buffered bytransistor 1408 to drive transistor 1409. Transistor 1409 may pull itscollector node high, turning on the indicator LED 1410 and soundingbeeper 1411.

Clock 1413 and amplifier 1412 may generate a clock signal (e.g., 32768Hz) that may be divided down by a certain factor (e.g., four) in clocks1414 and 1415 to generate a clock value (e.g., 8192 Hz) that may berequired to run the gate of mixer transistor 1404. In some embodiments,for example when operation of circuit 1400 is not needed, a high voltagelevel (e.g., greater than 3V) on ENABLE input 1416 may disable operationof circuit 1400 by holding clock 1415 in reset, such that mixertransistor 1404 does not run. It may be that no input can be detectedbecause the antenna input is floating, and thus the enable input may beused to terminate operation of locator circuit 1400 or portions thereof.This termination may occur in many instances, including for example,when the probe is imaging in association with a main unit, and when itis being used as a finder for another probe. In either instance, ENABLE1416 may be taken to a positive supply (e.g., greater than 3V) in orderto disable operation of circuit 1400. For example, ENABLE 1416 may bedriven from transistor 1417.

In the example circuit shown in FIG. 14, operational power supplycurrent of the above circuit may be about 7 μA, which in someembodiments may be low enough that the circuit can be connected to thebattery continuously without harm (e.g., battery capacity may beapproximately 1 amp-hour). In this example, even if the battery has beendepleted to 10% of its total capacity, enough energy would exist topower the circuit for more than 1.5 years. As a result, in someembodiments, the locator may be connected directly or indirectly to thebattery pack leads. Also, in some embodiments it may be that the locatordoes or does not have separate battery management control.

FIG. 15 is a block diagram of a circuit 1500 that provides externalsource functionality, for example in a passive locator environment.Circuit 1500 may be designed to emit a field to which locator circuit1500 may respond. Although FIG. 15 is an example of a specific circuit,it should be appreciated that this is just one example of such a circuitand does not preclude the use of other components in the circuit or evenother circuits. The components shown and discussed may not represent allof the components that may be used, but are limited for the purposes ofclarity and brevity.

As shown in FIG. 15, the external source used in the passive locator,for example, may begin operation when a user presses switch 1501 andprovides power (e.g., via battery 1515) to the remainder of circuit1500. In some embodiments, switch 1501 may be a momentary switch, suchthat the user may have to hold down switch 1501 for the circuit tointerrogate its surroundings. Having a momentary switch instead ofanother type of switch may facilitate circuit 1500 not using additionalpower accidentally, when not in use. Indicator 1502 may indicate to theuser that circuit 1500 is operating. Circuit 1500 may take on variousforms. For example, circuit 1500 may be built into the main unit, it maybe a hand-held module that docks in the main unit, but is removable tosearch for probes. Also, circuit 1500 may be integrated into a probe,such that one probe may be used to find another, etc.

In operation, the crystal oscillator 1503 output may be fed to a simpleprogrammable logic device (PLD) 1504 that may include clock dividers1505 and a counter 1506. In this example, a first clock divider maygenerate an 8213 Hz signal, that may be some frequency (e.g., 21 Hz)above a center frequency (e.g., 8192 Hz). This may create a simplesingle sideband (SSB) modulation at 21 Hz. The clock may be fed tocomponents 1507 and 1508, and cause them to alternately pull theiroutputs to some voltage (Vt) or ground. This may drive the series-tunedoutput circuit and stimulate the output antennae to emit a magneticfield at a frequency of 8213 Hz, for example.

Output antennae 1509 may have an open magnetic path, such that theirmagnetic flux couples through free space. The open magnetic path may benecessary to couple to the antenna of locator circuit 1500. Outputantennae 1509 may be of the same design as the receiving antennainductor of locator circuit 1500. Some embodiments may include threeoutput antennae because the coupling from transmitter to receiver may bedependent on the relative orientation of the two, in some embodiments.Therefore output antennae 1509 may be mounted in such a way that theirmagnetic axes may be mutually perpendicular.

The field generated by circuit 1500 may couple the transmitter andreceiver in proportion to the cosine of the angle between their centralmagnetic axes. For example, if the antenna is a solenoid, it is thecentral axis of the solenoid. As a result, in some embodiments, it maybe necessary to emit fields in a number of different orientations toensure that the transmitter magnetic axis is not substantiallyperpendicular to the receiver magnetic axis. In those embodiments thatemploy three mutually perpendicular axes of orientation in thetransmitter, the receiver axis may not be more than 54.7° from one ofthe axes of the three transmitter antennae. Therefore, PUD 1504 may usea divide-by-3 counter that sequences through three states on a 2 Hz timebase to sequentially stimulate the three antenna axes for 0.5 s each.

Some embodiments may use a transmitter power control 1516 to possiblyallow setting of an output drive level to the antennae. The output drivelevel may be set to a stimulus level that may be sufficient to bedetected by the locator circuit at about five meters, for example. Fivemeters may be of sufficient distance to allow finding probes within theimmediate vicinity of the user without extending the reach of the findertoo far. For example, it may not be of much use to extend the reach toofar because the probe needs to be within view or hearing of a user inorder to be found anyway. Of course, some embodiments may includetracking at a distance greater than five meters for other purposes.

Output antennae 1509 may be driven based on the state of counter 1505used in PLD 1504. Because in some embodiments output antennae 1509 maybe inductive, when the transmit drive to one of them becomesdisconnected, it will generate an inductive voltage spike as itdissipates any energy stored in its magnetic field. As a result,resistors 1511-1513 and diodes 1514 may be used to shunt this voltagespike to the power supplies and protect components 1507 and 1508.Resistors 1511-1513 a or other resistors also may be used to set the Qof the series tuned output circuits. In particular, the impedance of theoutput circuit 1510 at resonance may have a minimum of 10 ohms to allowthe drive current (and the proportional magnetic field) to besufficiently controlled.

Although circuit 1500 is shown connected to battery 1515, it should beappreciated that circuit 1500 may receive power from an AC power source.In some embodiments, circuit 1500 may use as much as 130 mA. In theseembodiments, it may be necessary for the battery must have substantialdrive capability. Also, because in some embodiments the circuit may notbe used for extended periods (e.g., more than a few minutes at a time)the total energy capacity of the battery may not need to be very high.For example, in some embodiments, a battery capacity of 100 mA-hours maysuffice. Also, it should be appreciated that these values are justestimates that may be changed, for example, if there is the possibilityof recharging, for example, while circuit 1500 is docked in the mainunit. For example, an even lower capacity battery may be sufficient.

In some embodiments, the data transmission rate may be based upon theproduct of a minimum acceptable frame rate and an amount of data perframe. Some embodiments may be required to deliver a minimum acceptableframe rate, for example, because of some external clinical requirements.In these embodiments, it may be that for a given data transmission rate,an amount of data per frame may be less than some maximum amount. Insome embodiments, if the amount of data per frame is assumed fixed, thedata transmission rate may be above some minimum value. Typically, theminimum frame rate may be set by the clinical requirements, and a numberof embodiments are contemplated to vary the amount of data per frame.Also, in these embodiments, various possible approaches are available togain different data transmission rates. In some embodiments, it may bedesirable to reduce frame rate in order to reduce the required datatransmission rate from the probe, for example.

In some embodiments, several hundred million bits of data may begenerated per frame. For example, a probe with center frequency Fc=6 MHzand 20 bits of baseband data spanning 4 cm (i.e., approximately 350samples), may produce 350×20 bits of data per transmit/receive elementcombination. Sparse array techniques may be used to limit the number oftransmit/receive element combinations per frame to approximately 2048.For a 480 Mbps data rate, the resulting frame rate for these exampleoperating parameters may be 480×10⁶/(350×20×2048)=33 fps.

It should be appreciated that some embodiments may be influenced byreduction of system power requirements. Also, some embodiments may makeit desirable to move functions between the probe, main unit and othercomponents, and vice versa, for example to perhaps reduce the size ofthe required circuitry in those devices. In those embodiments wherefunctionality is moved out of the probe, relatively higher bandwidthrequirements may be found. This reduction of bandwidth requirements maybe accomplished using a number of techniques contemplated by thedisclosed embodiments.

In certain contexts, these embodiments may be impacted by the fact thatthe communication link may be relatively shorter (e.g., 3 meters from anultrasound wireless probe to the main unit). Generally, some embodimentsmay make it desirable to reduce an amount of data communicated betweenthe probe (i.e., either wired or wireless), the main unit, and/or otherdevices. Such techniques may be desirable whether the system usessynthetic transmit focus techniques, acoustic transmit focus techniques,and/or some combination thereof.

Although certain methods are disclosed, it should be appreciated thatthe embodiments are not limited to such methods. Instead, the disclosedembodiments include numerous techniques to reduce data between theprobe, the main unit, and other devices. For example, certain of thecontemplated methods may manipulate system processes related toresolution, field of view, dynamic range, and/or any other parametersassociated with the image display and any other points throughout theprocessing chain. Such methods also may be, for example, based onvarious system components such as the transducer, signal processor,display, and the like. In some embodiments, the methods may involvedependency on certain user settings, including depth range, displayeddynamic range, and the like. Also, these data reduction techniques maybe dependent or independent on the type of ultrasound techniquesemployed, like acoustic transmit focusing, synthetic transmit focusing,beamforming and/or non-beamforming, etc.

The methods include, but are not limited to, tissue dynamic range,lateral resolution, region of interest, axial resolution, and color flowclutter to signal ratio (CSR). Although some of the methods may bediscussed in the context of synthetic transmit focus and/or acoustictransmit focus, it should be appreciated that the methods are not solimited, but may be applied to other techniques including a combinationof approaches. Also, the methods may include various imaging techniques,including color flow mode, B-mode imaging, spectral Doppler mode, etc.

With respect to tissue dynamic range, a displayed dynamic range, forexample, of a B-mode tissue image typically is selected by the user. Theparticular range is predetermined to be within some range made availableby the system. The dynamic range may refer to a ratio of the largestdisplayed signal level to the smallest visible level. In someembodiments, the system may provide a default dynamic range, dependingupon the particular application. In some embodiments, excess signaldynamic range may be carried through the signal processing path toaccommodate a maximum allowable setting (e.g., greater than 60 dB).

Because in some embodiments the displayed dynamic range may be limitedat some point in the image processing prior to display, it may bepossible to reduce the dynamic range earlier in the processing path.Reducing the dynamic range may allow for reduction of the required databandwidth. For example, dynamic range may be set to support just what isrequired to display the image at the selected setting, for example. Insome embodiments, this reduction may be accomplished without sacrificingany image quality, or with sacrificing a level of image quality that isacceptable to the user.

In some embodiments, dynamic range may be varied by mapping the digitaldata a different number or values. This, for example, may accomplishdata compression of the digital data. For example, the data compressionmay be lossless compression of the digital data. The mapping may beaccomplished by mapping one digital data value to a number and/ormapping more than one digital data value to a number. Also, the mappingmay be accomplished based on certain predetermined ranges, such that adigital data value within a first range may be mapped a certain way,while a digital data value within a second range may be mapped anotherway.

In some embodiments, the mapping techniques may include selecting aportion of the digital data and/or varying the selected portion over atime. The time over which the portion is varied may include a distancetraveled by the ultrasound echo wave, a displayed image, and a depth ofpenetration of the ultrasound interrogation wave. Also, the particularselection may be based on characteristics of ultrasound echo wave and/orcharacteristics of the digital data. The values may be represented by anumber of data bits, such that the selected portion of the digital datarepresents a number of bits at least equal to a number of bits of thedigital data. The technique may also include comparing a characteristicof the digital data to a predetermined threshold, and determining aportion of the digital data as a function of the predeterminedthreshold. The portion of the digital data may include a number of bitsof data, and a number of transmitted bits may be less than a number ofavailable bits.

In some embodiments, the dynamic range may vary throughout the imageprocessing. Just one example of such variation occurs with integrationor antenna gain, where the dynamic range of a beamformed signal may begreater than individual channel signals. The increase in dynamic rangemay be caused by an integration gain (IG) that is approximately equal to10LOG₁₀(N) dB, where N is the number of combined channels. In thoseembodiments that include typical phased array systems, N may representthe receive channels combined in the receive beamformer, for example. Inembodiments that include synthetic transmit focus techniques, N mayinclude the element combinations used for both transmit and receivefocusing, for example. In some embodiments, N typically will beapproximately an order of magnitude greater than a phased array system,or have a greater dynamic range of at least 10 dB.

It should also be appreciated that dynamic range may vary with depth ofpenetration of the interrogating wave. For example, as the requireddepth increases for the interrogating wave to hit a target, the strengthof the echoed wave may be reduced, for example, because of signalattenuation and transmit beam characteristics. As a result, in someembodiments, it may be that lower intensity echo signals requirerelatively less dynamic range than larger signals. As a result, it maybe desirable in some embodiments to adjust dynamic range to the varyingsignal requirements to reduce the required amount of data. For example,reducing the number of data bits for signal data in the far-field whereecho signals are the most attenuated, may permit greater data reduction.

In those embodiments that include phased array techniques, it may bethat beam intensity is a maximum at some focal point, yet decreasesfarther from the focal point. In those embodiments that include asynthetic transmit focus system, because unfocused or defocused transmitbeams may be used, the beam may be divergent with some near fieldeffects due to the fixed elevation focus and the element factor of thetransducer. Typically, with synthetic transmit focus, the echoed wavemay attenuate relatively more quickly and have relatively lowerintensity echoes compared to systems using focused transmit beams, forexample. There may be, however, an increase of dynamic range on thereceive side as a result of the dynamic transmit focusing used insynthetic transmit focus systems, for example.

Calculating required signal dynamic range depends on a channel signallevel, integration gain, and the displayed dynamic range, for example.Available signal dynamic range may be determined by subtracting noisefloor from peak signal level. In some embodiments, available signaldynamic range may be increased by the integration gain, for example, tolevels that may exceed the displayed dynamic range. Integration gain andavailable signal dynamic range may vary with depth, so a resultingcombined signal dynamic range also may be a function of depth. While theavailable signal dynamic range typically decreases with depth, theintegration gain may cause the dynamic range to increase with depth dueto an f-number and/or acceptance angle criterion, which is well known inthe art as referring to the ratio of the focal length of a lens (or lenssystem) to the effective diameter of its aperture. With respect toultrasound arrays, for example, the f-number may refer to the ratio ofthe focal distance to the width of the array aperture (typicallycontrolled by the number of active array elements or some weightingfunction applied across the aperture). Therefore, the aperture growslarger proportional to the distance from the transducer. For example,for an f-number of 2, the aperture width is set to half the focaldistance, so at a point 2 cm deep, a 1 cm aperture will be used. For anelement pitch of 1 mm, this corresponds to 10 active array elements.

In some embodiments, before displaying the image, the integrated anddetected image data may be compressed to a set dynamic range, such thatany excess dynamic range may be clipped to some maximum level. In thoseembodiments that use such clipping, it may be desirable to conserve dataand optimize the dynamic range and required signal bandwidth earlier inthe image processing. For example, dynamic range in excess of theclipping may be limited by appropriate gain adjustments and/or data bitallocation.

Other techniques may contemplate varying the dynamic range with depth,so as to accommodate just what is required. This may be accomplishedusing a number of techniques contemplated by the disclosed embodiments.Just two of such techniques may include applying gain adjustment basedon measured peak signal levels, and adjusting a data quantization (e.g.,number of bits) throughout the depth range. In some embodiments thesefunctions may be either fixed by being based on typical signal levelsand known display dynamic range, and/or dynamic so as to provide forwidely varying signal levels.

For some embodiments, the gain adjustment technique may include both ananalog time-gain control function, a digital gain control, and/or acombination thereof. In those embodiments where the analog-to-digitalconverters provide adequate dynamic range by themselves, it may bedesirable to set the analog time-gain control to a default setting withgains set as high as possible to prevent loss of smaller than expectedsignals. In these embodiments, any dynamic control may be provideddigitally prior to transmitting data from the probe to the main unit.Also, in some embodiments, digital signal levels may be monitored eitheron the probe, the main unit, and/or some other device. In someembodiments, because the main unit may allow for greater data processingcapabilities, it may be desirable to perform such processing at the mainunit. In these embodiments, the associated data may be passed, forexample via a resultant control table, from the main unit to the probeto establish the gain control function.

The gain control function may be specified as a fairly simple set oftransition points. For example, at more shallow penetration depths,signals may be set to a maximum dynamic range of approximately 10 bitsand shifted to some amplitude level based on peak signal levels. Someembodiments may permit, at a given range sample, the bit width to bedecreased and/or the range shifted down to accommodate the requirementsof the value of the range. In some embodiments, it may be that theprocess is continued throughout a part of or the entire depth range ofinterest. At greater depths, the signal may drop below some noise flooror minimum, such that a minimum number of bits may be required torepresent the data. Also, in some embodiments, it may be that when thesignal amplitude is either above or below some predetermined level ofthe gain control function, it is clipped.

FIG. 16 is a graphical depiction of the signal levels, integration gain,gain control factor, and attenuated signal levels over an 80 mm range.The example illustrated in FIG. 16 provides an illustration of tissuedynamic range based on synthetic transmit focus techniques having adivergent or defocused transmit beam. Although the example is providedin this context, the disclosed embodiments are not so limited, but maybe applied to other contexts including acoustic transmit focustechniques. Also, while the example provides values for the purposes ofclarity and brevity, it should be appreciated that any such values arecontemplated by the disclosed embodiments.

A maximum analog front-end gain is set such that the noise following theanalog-to-digital converter is approximately 7.5 dB above theanalog-to-digital converter noise floor. Also, the total front-end inaddition to analog-to-digital converter noise is 10 dB RMS. On average,the received echo signal plus noise in the near field occupies 60 dB andis attenuated at a constant rate of 1 dB/mm. It should be appreciatedthat these values may be fixed in the system and/or may be dynamicallycomputed by the system based on acquired signals. The displayed dynamicrange is set to 50 dB. There are 96 transducer elements and may bedecimated by a factor of 3, and there may be a maximum receive apertureof 48 elements. The transmit f-number is 1.5 and receive f-number is1.0. A maximum 10-bit limit is assigned to the channel data prior totransmission.

As shown in FIG. 16, because the noise floor is 10 dB at a gain of 0 dB,the skin-line dynamic range is 60−10=50 dB. Also, because 50 dB equalsthe display dynamic range, in some embodiments no gain adjustment isrequired. As shown in FIG. 16, at 10 mm, even though the signal levelhas dropped 10 dB, the integration gain has increased by 18 dB makingthe total dynamic range 50−10+18=58 dB. Because 8 dB may be above thedisplay range, some embodiments may be reduced by 8 dB. At 26 mm theintegration gain is almost 26 dB but the signal level has decreased toonly 34 dB so the effective dynamic range again equals 50 dB and, insome embodiments, no gain adjustment may be needed. Beyond 26 mm, theeffective dynamic range is less than 50 dB so the gain remains at themaximum of 0 dB.

In some embodiments, the signal level post-gain adjustment may determinethe required data. Typically, near the skin-line or surface of themedium, little dynamic range comes from the integration gain. As aresult, in some embodiments, most of the dynamic range may be carried inthe main channel data, and perhaps require more data. As the signallevels decrease, in some embodiments less data is required. As shown inFIG. 16, eventually at 48 mm, the signal drops below the noise floor andonly the minimum number of bits may be required, in this case 3 bits.

FIG. 17 is a graphical depiction of the number of bits of data requiredover a depth range of 0 to 80 mm for the parameters discussed withreference to FIG. 16. As shown in FIG. 17, in this example, the numberof required bits decreases monotonically with depth. Of course, thisgraph does not represent all imaging conditions, and the signal levelsmay peak higher at a point beyond the shallowest depth. For example,signal levels may peak higher at a point beyond the shallowest depth ina focused transmit beam context. Also, in some embodiments, signals thatfall below 0 dB may be clipped. In addition, any signals reaching abovea range allowed by the number of data bits provided may be clipped tothe maximum attainable level, in some embodiments.

With respect to lateral resolution, a total number of data bitstransferred from the probe to the main unit or other device may dependon the bit width provided (B), the number of receive channels pertransmit (R), and the number of transmit events (T). Both I & Qcomponents may also be represented, and may add another factor of two.The resulting calculation is as follows: Total Bits=2×B×T×R.

In some embodiments, the aperture growth (or the number of transducerelements used) may be varied based on the transmit and receiveacceptance angles. As a result, in some embodiments, not all thenear-field data may be required for each transmission. Also, in someembodiments, for each transmit event data from receive channelsextending beyond the sum of the transmit and receive apertures may notneed to be sent to the main unit, because they are outside the aperturebounds. Therefore, data may be reduced in these embodiments because someof the larger bit-width near-field data need not be sent to the mainunit.

Also, some embodiments may limit the maximum aperture size and reducethe amount of data sent from the probe to the main unit. Because lateralresolution typically is proportional to aperture size, some embodimentsmay reduce lateral resolution to permit greater data bandwidth. This maybe accomplished, for example, by restricting the maximum aperture sizeand/or the acceptance angle.

FIG. 18 is a graphical depiction of the total amount of data requiredfrom the probe to the main unit with respect to depth, considering theacceptance angle and edge effects. When transmitting at or near theedges of the transducer array, the receive aperture may be truncated. Asa result, in some embodiments, less data may be sent from the probe tothe main unit relating to edge element transmissions. FIG. 18illustrates the sum of the transmit and receive channels for an entireimage frame. As shown in FIG. 18, the dashed line represents the totaldata assuming the maximum number of bits (10), while the solid lineincorporates the bit width optimization as discussed with reference toFIG. 17.

FIG. 18 illustrates that with no savings from aperture reduction, therewould be a required 3.75 Kbytes over the full depth range. The aperturerestrictions results in a 7% reduction in data, while the bit widthminimization results in a 49% reduction of the aperture-restricted dataand a total reduction of 52% compared to the non-reduced data. In termsof transmitted frames per second (fps), the maximum achievable framerate with no data reduction is 37 fps, while with data reduction a framerate of 78 fps is achievable.

A region of interest (ROI) of an imaging system may refer to a geometricdimension represented by the displayed image. For example, for a lineararray, an image's width typically extends to the edges of the array but,in some embodiments, may be steered to go beyond the edges. For example,with phased array systems, beams may be steered such that the beamvectors converge at a relatively common apex. In some embodiments, amaximum steering angle may be dependent on probe frequency and elementpitch.

With respect to B-mode imaging, for example, an image may be formed froma linear array probe with little or no steering. The depth range of theimage may be considered to be the distance between the shallowest imagepoint and the deepest, for example. Signal acquisition time may beproportional to the depth range, and the depth range may be adetermining factor in a number of data samples that are transferred fromthe probe to the main unit. In some embodiments, in order to minimizedata, it may not be required to transfer data that does not contributeto the formation of image pixels. Therefore, data acquired either beforea minimum required sample time and/or after a maximum required time maynot need to be transferred to the system in some embodiments.

In some embodiments, factors that may be considered in signalacquisition time may include consideration of path lengths. For example,signal acquisition time may be based upon an echo path length of theclosest element to the minimum depth point (path_min), and/or an echopath length of the furthest element to the maximum depth point(path_max). These path lengths may depend on a number of various factorsincluding steering angle, aperture size, and/or aperture growth rate,for example.

A maximum acquisition time may be proportional to a difference betweenthe shortest and longest echo path lengths (i.e., path_max_path_min). Insome embodiments, the data sample range transferred from the probe tothe main unit may be constrained to this time period so as to provideoptimal wireless bandwidth conservation, for example.

FIG. 19 is an illustration of an example image ROI for a linear arraytransducer with a 30 mm width. The values defined with reference to FIG.19 provide just one example for the purpose of clarity and brevity andare not meant to be exclusive values. In some embodiments the minimumpath length (path_min) is the distance of the perpendicular line fromthe transducer to the shallowest image ROI point of 20 mm, and themaximum path length (path_mat) is the distance from an edge element tothe furthest image ROI point from it. As shown in FIG. 19, the f-numberis set to 1.0 so the aperture may not be completely on at the ROI bottomdepth of 40 mm. While there may be a dependence on aperture growth itmay be to a substantially lesser degree.

The acceptance angle (Θ) is equal to tan⁻¹ (30/60)=26.56°, and thepath_max distance is 40/cos(Θ)=44.72 mm. Therefore, the maximumacquisition time is as follows:acquisition_time=1.3path_max-path_min)=1.3(44.72−20)=32.1 μs, where 1.3is the roundtrip travel time of sound in μs/mm. If the ROI is extendedto the skin-line or surface of the medium, an acquisition time may be1.3×44.72=58.1 μs. As a result, in some embodiments, with eitherstarting depth, the elements have a same minimum path length, but withperhaps different maximum path lengths. For example, when transmittingat the center element location, the path_max value from the skin-linemay be √{square root over (15²+40²)}=42.7 mm, giving an acquisition timeof 1.3×42.7=55.5 μs, or 4.5% less than the edge element time.

Therefore, it may be desirable in some embodiments to specify individualacquisition times for each transmit/receive transducer elementcombination, perhaps to minimize an amount of data to be transferredbetween the probe to the main unit or other device.

Communication bandwidth may place an upper limit on axial resolution,because the displayed resolution may be determined by various parametersincluding transducer characteristics and the display device. Forexample, it is well understood by those skilled in the art that theNyquist criterion prescribes that a desirable resolution may be attainedby adequately sampling a received echo signal by at least twice itsbandwidth. For example, with quadrature sampling using in-phase andquadrature components, each component may be sampled at a rate equal toor greater than the signal bandwidth. Bandpass sampling techniques mayproduce a quadrature baseband signal from each receiver channel that isideally sampled at a rate adequate to capture the information contentprovided by the transducer bandwidth. Therefore, in some embodiments,producing data at this rate is relatively efficient because it producesa minimum amount of data necessary to avoid loss of image quality. Otherembodiments may use over-sampling techniques to provide benefits likegreater SNR, at the expense of producing more data than perhaps needed.Therefore, in just some embodiments, in order to minimize data requiredto be transferred from the probe to the main unit, the probe maytransfer baseband data sampled at less than or equal to the idealsampling rate based on the transducer's bandwidth.

The baseband representation of the data signal may retain the fullsignal bandwidth with the energy centered perhaps around zero frequency(DC) instead of Fc. The baseband signal may be considered in analyticform as I+j*Q where I is the in-phase component and Q is the quadraturecomponent. It should be appreciated that the baseband signal may bederived by quadrature demodulation of the data signal. This may beaccomplished, for example, using a complex mixer followed by a low-passfilter on the I and Q components.

In those embodiments where baseband conversion is performed prior toanalog-to-digital conversion, the analog-to-digital converter samplingrate may be less than that required to capture the data signalinformation. For example, for a data signal with 100% bandwidth, thesampling rate may be at least 3 times Fc (e.g., to satisfy the Nyquistcriterion). In some embodiments, baseband signal may need to be sampledat Fc for each of the analytic components for a combined sampling rateof 2 times Fc. Therefore, the sampled data may produce 50% more datasamples than baseband sampled data. It should be appreciated that theincrease may be greater yet for smaller probe bandwidths.

Some embodiments may provide baseband conversion using a quadraturesampling, well known to those skilled in the art. For example,quadrature sampling may be conducted by sampling the data signal at 4times Fc followed by decimation of the other pair of samples. In thisexample, remaining sample pairs may approximately represent I and Qbaseband sample pairs. Although this embodiment, known in the art assecond-order sampling, may be simplistic it also may reduce an amounthardware and software complexity, which may be desirable in someembodiments. Also, in some embodiments using second-order sampling,component (e.g., probe) complexity and circuitry may be minimized viamultiplexing techniques, like time and frequency techniques. Forexample, two receiver channels may be multiplexed into a singleanalog-to-digital converter on alternate pairs of I and Q samples. Viamultiplexing techniques the data may be arranged, interleaved and/ormultiplexed using a number of techniques. Some of the multiplexingtechniques may serve to reduce data bandwidth as well as serve otherobjectives. For example, data may be manipulated after converting thereceived echoed ultrasound wave to digital data and/or data may bemanipulated to converting the received echoed ultrasound wave to digitaldata. The multiplexing techniques may include time-divisionmultiplexing, frequency-division multiplexing, code-divisionmultiplexing, and/or pulse width-division multiplexing. The data alsomay be interleaved as a function of time, position of transducerchannels, and/or data bit position.

Interpolation may be used to overcome some inherent time misalignment ofI and Q components. In some embodiments, such sample interpolation maybe used in combination with other sample interpolation techniques, likecoherence preservation techniques.

Third-order sampling techniques also may be used to improve the timealignment of I and Q sample pairs. For example, this third-ordersampling technique may be implemented by subtracting the 180° phasesample from the 0° phase sample and dividing the result by 2 to form thein-phase component. The quadrature component may be acquired as the 90°phase sample just as in second-order sampling.

Some embodiments may maintain greater axial resolution with relativelylow drive voltages. This may be accomplished using a number oftechniques, including for example, coded transmitted excitations thatuse a relatively large time-bandwidth product codes. In order to ensuregreater axial resolution under relatively basic excitation conditions,an acoustic pulse provided by the transmitting transducer may be animpulse response. In those embodiments that employ coded excitationtechniques, the acoustic pulse may be relatively longer than thetransducer's typical impulse response. For example, coded excitation maytransmit a long “chirp” or sequences of orthogonal signals, known bythose skilled in the art as Golay codes. The received echoes may becorrelated with a reference waveform to regain axial resolution of ashort pulse, for example. A relatively longer pulse provided by codedexcitation may increase signal-to-noise ratio that may otherwise besacrificed due to other factors (e.g., general synthetic transmit focustechniques).

In some embodiments, transducer bandwidth may not be matched to a finaldisplay resolution. For example, a single transducer element sampledusing bandpass sampling with a center frequency (Fc) of 6 MHz, may havea bandpass sampling rate of approximately 6 MHz. In some embodiments itmay be that this sampling rate would be adequate if the signal energywas negligible at frequencies lower than 3 and greater than 9 MHz, forexample. Also, the 6 MHz rate with an image ROI from the skin-line to 40mm may yield a worst-case number of samples of 58.1×6=349 samples, wherethe 58.1 μs was derived in the above ROI example. In some embodiments,this may be reduced by, for example, applying different acquisitiontimes to the various element combinations and/or to each transmitlocation.

In this example, while it may be necessary to acquire and transferapproximately 349 samples per element combination, the verticaldimension of the displayed image may require just 1.3×40×6=312 samples.If, as in some embodiments, the samples can be mapped directly todisplayed image pixels, this would require a display pixel density of312/40=7.8 pixels/mm. In other embodiments, it may be desirable toensure square pixels, such that the 30 mm wide image may require 234horizontal columns of pixels. The 349×234 pixel grid may represent amaximum resolution supported by a particular transducer. Of course,depending on the properties of the display, this image may or may notprovide a desirable perceptible resolution from a typical viewingdistance. Therefore, for displays with very high pixel densities, forexample, in some embodiments it may be desirable to scale the image upto larger pixel dimensions. This may be accomplished using varioustechniques, including for example, interpolation.

If in the example, an image ROI includes a depth range from theskin-line to 80 mm, it may be that twice the number of samples (i.e.,624) may be produced at the same 6 MHz sampling rate. Of course, in someembodiments the displayed image may have a span on the screen that isless than 624 pixels, such that the signal bandwidth may be reduced andthe data resampled at a more suitable (e.g., lower) rate. Alternatively,in some embodiments, it may be desirable instead or in addition totrade-off axial resolution for reduced wireless data rates at relativelylarger depth ranges in order to maintain higher frame-rates. In eithercase, typically it may be desirable to perform the data rate reductionearly in the system processing to avoid transferring and managing moredata than is necessary to attain the desired image resolution. This maybe accomplished in some embodiments using a data resampler functionfollowing the analog-to-digital converter, for example, for eachreceiver channel within the probe.

The following example provides just one scenario contemplated by thedisclosed embodiments. In just this one example, a 2D ultrasound imagedisplay may be composed of a pixel grid with a spacing based on theproperties of the display device and the image acquisition parameters.For example, a typical display device may have a maximum pixelresolution of 800×600. The image may be created to fit a portion of thisdisplay grid. The imaging distance as a result of the pixel spacing maybe determined by a relationship between the data rate (e.g., samplingrate of the data presented to the display) and the speed of sound (e.g.,approximately 1540 m/s in a human body, for example). This relationshipmay be defined as: D=c÷(2×R), where c is the one-way speed of sound, Ris the data rate, and the factor of 2 derives from the roundtrip travelof the pulse. The relationship may be considered in the context of apulse traveling from a single element in a direction perpendicular tothe transducer array. For purposes of this one example, it may beconsidered that the returning echo signal is converted to baseband,envelope-detected, sampled periodically, and mapped to the display in adirect (i.e., sample-to-pixel) relationship. If the sampling rate (R) is6 MHz and the image display is composed of a column of 300 pixels, therepresentative image depth range would be: 300×1540÷(2×6)=38.5 mm.

In those embodiments where it may be desirable to display twice thatdepth range, it can be seen from this relationship that either twice thenumber of samples may be acquired corresponding to twice the number ofpixels, and/or the sampling rate may be reduced by a factor of 2.

In some embodiments the relationship between the sampling rate andsignal bandwidth may be manipulated. As is well known to those skilledin the art, sampling theory designates the signal sampling rate to be atleast twice the signal bandwidth (i.e., Nyquist rate). In someembodiments, this may avoid corrupting the resultant signal by aphenomenon well known to those skilled in the art as aliasing. Forexample, in some embodiments where the signal of interest is representedas a quadrature pair of signal components, the sampling rate of eachquadrature component may be equal to or greater than the bandwidthrepresented by the component pair. Therefore, some embodiments mayinclude a relationship between transducer bandwidth and displayresolution.

In some embodiments it may be that the signal may be sampled at adifferent rate than the Nyquist rate, for example, unless the quadraturesignal bandwidth is confined to that rate. For example, although it maybe sufficient to sample at a rate higher than the transducer bandwidthand display the full signal resolution for even the deepest desireddepth range, it should be appreciated that in some embodiments, this maybe impacted by the resolution of the display device. For example, insome embodiments the display may be able to display less than a requirednumber of pixels for full resolution imaging. It some embodiments, itmay be desirable to reduce some resolution if larger depth range isdesired, for example, by filtering the signal to a desired bandwidthand/or resampling the signal to a desired rate. In some embodiments suchresampling may occur within the main unit (e.g., after the beamformer),the probe and/or some other device.

Resampling typically is a linear process, such that output samples maybe formed as linear combinations of neighboring input samples through afiltering process. Also, it may be that beamforming is linear, becauseit may include linear combinations of a set of time-delayed signals. Itshould be appreciated in these embodiments that superposition may holdfor linear systems, such that resampling each data sequence prior tobeamforming, for example, may be analogous to resampling after. In someembodiments, it may be desirable to perform resampling as early aspossible in the processing.

Data resampling may be limited to rational numbers (e.g., P/Q).Resampling to a rate of P/Q may be accomplished by first up-sampling bya factor of P by zero-padding the data sequence with P-1 zeros. Azero-padded sequence (XP) is shown as follows for P=4:

X=X₁ X₂ X₃ X₄ X₅ X₆

XP=X₁ 0 0 0 X₂ 0 0 0 X₃ 0 0 0 X₄ 0 0 0 X₅ 0 0 0 X₆ 0 0 0

In some embodiments, a zero-padded sequence may be filtered with afinite-impulse response (FIR) filter, for example. The filtercharacteristics may be chosen as a function of desired data bandwidthand/or resampling factors. The sequence XPF below represents the XPsequence described above with the zero samples altered due to thefilter. In some embodiments, it should be appreciated that the originalsignal samples may or may not be altered by the filter, although shownhere as unaltered.

XPF=X₁ X₁₁ X₁₂ X₁₃ X₂ X₂₁ X₂₂ X₂₃ X₃ X₃₁ X₃₂ X₃₃ X₄ X₄₁ X₄₂ X₄₃

In some embodiments, the filtered sequence may be decimated in variousways, including for example, by discarding Q-1 samples after a retainedsample, resulting in the final desired data rate. The decimated sequenceis shown, in just one example, for Q=3 and the resulting rate of 4/3 theoriginal data rate.

XPFD=X₁ X₁₃ X₂₂ X₃₁ X₄ X₄₃ X₅₂ X₆₁

For color flow data acquisition, front-end gains may be set at a maximumthroughout most of a field of view. In some embodiments, for example,such a value may provide optimum sensitivity of red blood cell echowaves. Also, some signal saturation around strong reflectors may beacceptable, for example, where some arbitration may be provided toreject artifacts. With color flow techniques, the data signal may carryboth tissue-level echoes or clutter, and blood echoes. For example, insome embodiments, clutter-to-signal ratio (CSR) may be approximately 60dB. In some embodiments, the clutter filter may reduce dynamic range.

Some embodiments may reduce color flow data via clutter filtering, forexample, prior to wireless data transfer from the probe. This may beperformed, for example, with beamformed, non-beamformed, and other typesof data. Color flow clutter filters may include high-pass filtercharacteristics. For example, color flow clutter filters may beimplemented with a finite impulse response (FIR). Such embodiments mayminimize filter settling time, because color flow usually operates withrelatively short data ensembles.

An example filter may be a single DC canceller characterized asY(n)=X(n)−X(n−1), where X(n) is the input signal at time “n” and Y(n) isthe filtered output. Such a filter may provide a single zero at DC and aslow roll-off, high-pass frequency response, well known to those skilledin the art. Some embodiments may use such an approach because of itsease of implementation, need for just a single storage state, and justone settling pulse.

Other embodiments may use a similar design that provides two zeros atDC, called a double canceller, and implemented asY(n)=X(n)−2X(n−1)+X(n−2), where X(n) is the input signal at time “n” andY(n) is the filtered output. The double canceller filter may providegreater low frequency clutter attenuation and greater transientrejection. Also, some embodiments may implement color flow in acontinuous acquisition so as to allow the use of filters withsignificantly longer settling times. In these embodiments, a first-orderDIR filter may be used described as (1−α)Y(n)=X(n)−X(n−1)+αY(n−1), whereX(n) is the input signal at time “n” and Y(n) is the filtered output.This filter may provide a sharper response than either FIR filter, butwith similar computational complexity and storage requirements as thedouble canceller.

In some embodiments, quantization may be more difficult to manage withIIR type filters. In some embodiments, an IIR with two zeros at DC mayprovide greater transient cancellation. The length of the transient andsteepness of the cutoff may be proportional to a (i.e., larger arequires longer settling but provides steepest roll-off).

It should be appreciated that the discussion of filters is not limitedand many other filters may be used, some with greater hardwarecomplexity and storage requirements. Also, some embodiments mayimplement just a part of the overall clutter filter in the probe toprovide most of the attenuation required to reduce the signal dynamicrange, while performing any remaining filtering in the main unit. Anycombination thereof is contemplated by the disclosed embodiments.

Embodiments that use continuous acquisition may reduce or eliminateusual limitations on clutter filtering, well known to those skilled inthe art. For example, filters may be designed specifically for transientsuppression. For continuous acquisition color flow, greater designfreedom is recognized and may allow for a variety of different filterdesign methodologies.

In some embodiments, data collection methods may vary. For example, onemethod that may be used is to gather a single frame of data sequentiallyas quickly as possible to minimize phase errors across the frame. Also,in some embodiments, it may be desirable to continue data collectionregardless of interruptions in the data transfer, while in otherembodiments it may be desirable to cease data collection.

One way to manage data flow from the data collection process to the datatransmission process may be to use a “ping-pong” buffer (e.g., twoframes deep) to store entire frames of data. A ping-pong buffer may beimplemented using a variety of standard random access memory (RAM)storage devices, for example. One alternative to a ping-pong buffer maybe a first-in-first-out (FFO) storage device, for example. In the caseof a ping-pong buffer, the data collection process may continue at amaximum rate until a full frame is acquired. If the data transmissionprocess is slower than the data collection process, the data collectionmay fill the second frame buffer before the first is emptied. In thiscase, data collection may be stopped after completing that frame, andmay wait until one of the frames of the ping-pong buffer is emptied(e.g., transmitted), such that it is ready to accept an entire frame ofnew data, for example, gathered at the maximum rate set by thecollection process.

FIG. 21 is a timing diagram 2100 illustrating the acquisition of framesof data, using two methods 2101 and 2102. In method 2101, acquisitionmay be spread out over a frame period with each transmission periodevenly divided over the available frame time. In method 2102, timebetween transmissions may be shortened so that the frame acquisition mayoccur in a compressed time period, while the average data rate over aframe period may be the same or substantially similar to method 2101.Method 2102 is allowed by frame buffer.

In some embodiments, where bandwidth restricts a frame rate by a factorof two or more, for example, it may be advantageous to acquire multipledata sets and combine the data within the probe, and/or some otherdevice, before transmission to the main unit. This coherent combinationmay provide improved signal-to-noise ratio and/or some other imageenhancement.

In some embodiments, the communication medium or link may not provideconsistent bandwidth. In these embodiments, it may be desirable toadaptively adjust data acquisition parameters in response to theavailable bandwidth. These parameters may include, but are not limitedto, acquisition frame rate, transmit aperture size, receive aperturesize, and/or sparsity of transmit and/or receive apertures.

In addition, coherent combination for improved signal-to-noise ratio maybe dynamically controlled in response to the available bandwidth. FIG.20 provides a block diagram to provide such dynamic control using aping-pong frame buffer.

With any wired and/or wireless link there exists a possibility ofinterference that may cause the communication link to be lost, at leasttemporarily. One way to accommodate and prevent such loss of data isthrough packetization techniques so as to allow data to be recoveredfrom a temporary loss of signal by re-transmitting the lost datapackets. While the data is eventually re-transmitted successfully, itmay increase the amount of data transfer and the rate at which it istransferred.

In those embodiments that use acoustic transmit focus techniques, it maybe that an entire frame of data is captured sequentially as fast aspossible to minimize phase errors across the frame. In theseembodiments, it may be undesirable to stop the data collection processin response to interruptions in the data transfer. One possible solutioncontemplated by the disclosed embodiments is to use a ping-pong buffer(also known as a double buffer) for entire frames of data. In this way,the data collection process may continue at a maximum rate until a fullframe is acquired. If the data transmission process becomes slower thanthe data collection process, the data collection may, at some point,fill the second frame buffer before the first is emptied. In this case,data collection may be stopped after filling the second frame, and maywait until one of the frames of the ping-pong buffer is emptied (e.g.,transmitted), and is ready to accept an entire frame of new data,gathered at the maximum rate set by the collection process. Of course,other alternatives are contemplated by the disclosed embodiments,including using a larger ping-pong buffer and/or using memory from otherparts of the system. Also, instead or in addition to the ping-pongbuffer, a first-in-first-out (FIFO) memory device may be used that islarge enough to accommodate two entire frames, and with a means ofdetecting when there is enough room in the FIFO to hold an entire frameof data.

Referring to FIG. 20, a feedback loop may be used to implement suchmethods. As shown in FIG. 20, a throttle signal shown on the diagram mayinstruct the data merger and buffer control as to when the wirelessinterface can and cannot accept data. For example, if the throttleprevents a frame of data from being transmitted at its maximum possiblerate (i.e., the acquisition rate), the buffer control may informacquisition control to adjust its frame acquisition period accordingly.FIG. 22 is a timing diagram 2200 illustrating this frame adjustment.

FIG. 23 is a chart representing a sequence of writes and reads to aping-pong frame buffer for a frame of 5 samples, for example. As shownin FIG. 23, at time units 1 through 5, the 5 frame samples are writtento frame buffer addresses 1 a through 5 a, substantially consecutively.Similarly, at time units 6 through 10, the next 5 frame samples arewritten to frame buffer addresses 1 b through 5 b, where a and brepresent the two pages of the ping-pong buffer. Once the first fullframe of data has been written to the buffer, reading of the buffer maycommence as indicated at time unit 6. In this example, the first framerequires twice as long to read out than to write with each addresspersisting for 2 time units. During time units 11 through 15, the writeside of the buffer is throttled (as indicated by the letter T) whilewaiting for the first frame to be completely read out. At time units 16through 20, the third acquired frame is written to addresses 1 a through5 a. The read out of the second acquired frame begins at time unit 16immediately after the read out of the first acquired frame. Startingwith the forth sample, the addresses persist for 4 time units instead of2 indicating, perhaps, a decrease in the data transmission rate. Thethrottle condition exists for time units 21 through 29, 4 units longerthan the previous throttle period. Entire frames of data may be writtenin just 5 consecutive time units indicating that data acquisition may beconfined to a 5 time unit interval even though the acquisition frameperiod is longer and variable.

In some embodiments, acquisition control may be instructed to changeother acquisition parameters. For example, with respect to syntheticreceive aperture imaging, multiple transmissions may be required tocollect a receive aperture. In response to the throttle signal,acquisition control may be made to reduce the receive aperture size and,therefore, fire fewer transmissions so as to reduce an amount of datanecessary to send to the main unit and/or some other device.

In these embodiments, the main unit or the other device may require someinformation regarding the receive aperture size reduction for itsbeamformation and/or pixelformation processing, for example. Therefore,this information may be included in a control data sent along with theacquired image data, for example. It should be appreciated that variousother acquisition parameters may be adjusted to achieve the same effect,and are contemplated by the disclosed embodiments.

While the embodiments have been described in connection with variousembodiments of the various figures, it is to be understood that othersimilar embodiments may be used or modifications and additions may bemade to the described embodiment for performing the same function of thedisclosed embodiments without deviating therefrom. Therefore, thedisclosed embodiments should not be limited to any single embodiment,but rather should be construed in breadth and scope in accordance withthe appended claims.

1. A system for conducting ultrasound interrogation of a medium,comprising: a main unit; a remote unit; a first communication channelfor communicating ultrasound data with the main unit and the remoteunit, wherein the first communication channel is wireless; and a secondcommunication channel for communicating with the main unit and theremote unit.
 2. The system of claim 1, wherein the second communicationchannel is at least one of the following: wireless and wired.
 3. Thesystem of claim 1, wherein the ultrasound data communicated by the firstwireless communication channel is digital.
 4. The system of claim 1,wherein the second communication channel communicates digital ultrasounddata with the main unit and the remote unit.
 5. The system of claim 1,wherein the second communication channel communicates control data withthe main unit and the remote unit.
 6. The system of claim 1, wherein thesecond communication channel communicates different digital ultrasounddata than the first wireless communication channel.
 7. The system ofclaim 1, wherein the second communication channel communicates at leasta portion of the digital ultrasound data communicated on the firstwireless communication channel.
 8. The system of claim 1, wherein thesecond communication channel includes different communicationcharacteristics than the first wireless communication channel.
 9. Thesystem of claim 1, wherein the communication characteristics include atleast one of the following: bandwidth capacity, transmission rate,transmission protocol, operating frequency, orthogonal relationship withrespect to one another, and temporal interleaving.
 10. The system ofclaim 1, wherein the second communication channel cooperates withcommunication on the first wireless communication channel to increase atransfer rate of the digital ultrasound data.
 11. The system of claim 1,wherein the second communication channel cooperates with communicationon the first wireless communication channel to minimize a transfer oferrors of the digital ultrasound data.
 12. The system of claim 1,wherein the second communication channel provides a greater directionalcommunication path than the first wireless communication channel. 13.The system of claim 1, wherein the second communication channel allowsthe main unit to initiate communication with the remote unit.
 14. Thesystem of claim 1, wherein the second communication channel allows theremote unit to initiate communication with the main unit.
 15. The systemof claim 1, wherein at least one of the main unit and remote unitmultiplexes data communicated on the first and second communicationchannels using at least one of the following techniques: time-divisionmultiplexing, frequency-division multiplexing, code-divisionmultiplexing, and pulse width-division multiplexing.
 16. The system ofclaim 15, wherein the data is multiplexed as a function of at least oneof the following: time, position of communication channels, and data bitposition.
 17. The system of claim 1, wherein the remote unit forms animage frame from the data, storing the data, and transmitting the dataafter at least one image frame of data is stored.
 18. The system ofclaim 1, wherein at least one of the main unit and the remote unitreceives configuration information from the remote unit, wherein theconfiguration information comprises at least one of the following: powerstatus, designation of device, type of device, frequency range, arrayconfiguration, power warnings, capability of a remote unit, quality oftransmission of digital data, quantity of errors in transmission ofdigital data, availability of power required for transmission of digitaldata, change in transmission rate, completion of transmission, qualityof data transmission, look-up tables, programming code for fieldprogrammable gate arrays and microcontrollers, transmissioncharacteristics of the non-beamformed ultrasound wave, processingcharacteristics of the echoed ultrasound wave, processingcharacteristics of the digital data, and transmission characteristics ofthe digital data.
 19. The system of claim 1, wherein at least one of themain unit and the remote unit adjusts a transmission rate on at leastone of the communication channels as a function of a minimum acceptablerate of displaying an image frame and an amount of data per image frame.20. The system of claim 1, wherein at least one of the main unit and theremote unit reduces a bandwidth of the data communicated on at least oneof the channels by at least one of the following: quadrature sampling,second order sampling, and third order sampling.
 21. The system of claim1, wherein at least one of the main unit and the remote unit transmits aunique identifier with the data, wherein the unique identifier is usedfor at least one of the following: initiating communication with theremote unit, synchronizing communication with the remote unit, andensuring communication with a predetermined remote unit.
 22. The systemof claim 1, wherein the first communication channel transmits the data adistance of less than 3 meters.
 23. The system of claim 1, wherein thedata is communicated at a rate that varies with at least one of thefollowing: capability of the remote unit, power status of the remoteunit, capability of the main unit, power status of the main unit,frequency range, array configuration, power warnings, quality oftransmission of the data, quantity of errors in transmission of thedata, availability of power of the main unit, availability of power ofthe remote unit, a change in transmission rate, and transmissioncharacteristics of the data.
 24. A method for conducting ultrasoundinterrogation of a medium, comprising: communicating ultrasound dataover a first communication channel with a main unit and a remote unit,wherein the first communication channel is wireless; and communicatingultrasound data over a second communication channel with the main unitand the remote unit.
 25. The method of claim 24, wherein the secondcommunication channel is at least one of the following: wireless andwired.
 26. The method of claim 24, further comprising communicatingdigital ultrasound data with the first wireless communication channel.27. The method of claim 24, further comprising communicating digitalultrasound data with the main unit and the remote unit via the secondcommunication channel.
 28. The method of claim 24, further comprisingcommunicating control data with the main unit and the remote unit viathe second communication channel.
 29. The method of claim 24, furthercomprising communicating digital ultrasound data via the secondcommunication channel that is different than digital ultrasound datacommunicated with the first wireless communication channel.
 30. Themethod of claim 24, further comprising communicating at least a portionof the digital ultrasound data the second communication channel that iscommunicated on the first wireless communication channel.
 31. The methodof claim 24, wherein the second communication channel includes differentcommunication characteristics than the first wireless communicationchannel.
 32. The method of claim 24, wherein the communicationcharacteristics include at least one of the following: bandwidthcapacity, transmission rate, transmission protocol, operating frequency,orthogonal relationship with respect to one another, and temporalinterleaving.
 33. The method of claim 24, further comprising the secondcommunication channel cooperating with communication on the firstwireless communication channel to increase a transfer rate of thedigital ultrasound data.
 34. The method of claim 24, further comprisingthe second communication channel cooperating with communication on thefirst wireless communication channel to minimize a transfer of errors ofthe digital ultrasound data.
 35. The method of claim 24, furthercomprising providing a greater directional communication path with thesecond communication channel than the first wireless communicationchannel.
 36. The method of claim 24, further comprising initiatingcommunication with the remote unit via the second communication channel.37. The method of claim 24, further comprising initiating communicationbetween the remote unit and the main unit via the second communicationchannel.
 38. The method of claim 24, further comprising multiplexingdata communicated on the first and second communication channels usingat least one of the following techniques: time-division multiplexing,frequency-division multiplexing, code-division multiplexing, and pulsewidth-division multiplexing.
 39. The method of claim 38, wherein thedata is multiplexed as a function of at least one of the following:time, position of communication channels, and data bit position.
 40. Themethod of claim 24, further comprising forming an image frame from thedata, storing the data, and transmitting the data after at least oneimage frame of data is stored.
 41. The method of claim 24, furthercomprising receiving configuration information from the remote unit,wherein the configuration information comprises at least one of thefollowing: power status, designation of device, type of device,frequency range, array configuration, power warnings, capability of aremote unit, quality of transmission of digital data, quantity of errorsin transmission of digital data, availability of power required fortransmission of digital data, change in transmission rate, completion oftransmission, quality of data transmission, look-up tables, programmingcode for field programmable gate arrays and microcontrollers,transmission characteristics of the non-beamformed ultrasound wave,processing characteristics of the echoed ultrasound wave, processingcharacteristics of the digital data, and transmission characteristics ofthe digital data.
 42. The method of claim 24, further comprisingadjusting a transmission rate on at least one of the communicationchannels as a function of a minimum acceptable rate of displaying animage frame and an amount of data per image frame.
 43. The method ofclaim 24, further comprising reducing a bandwidth of the datacommunicated on at least one of the channels by at least one of thefollowing: quadrature sampling, second order sampling, and third ordersampling.
 44. The method of claim 24, further comprising transmitting aunique identifier with the data, wherein the unique identifier is usedfor at least one of the following: initiating communication with theremote unit, synchronizing communication with the remote unit, andensuring communication with a predetermined remote unit.
 45. The methodof claim 24, wherein the first communication channel transmits the dataa distance of less than 3 meters.
 46. The method of claim 24, furthercomprising varying a rate that the data is communicated with at leastone of the following: capability of the remote unit, power status of theremote unit, capability of the main unit, power status of the main unit,frequency range, array configuration, power warnings, quality oftransmission of the data, quantity of errors in transmission of thedata, availability of power of the main unit, availability of power ofthe remote unit, a change in transmission rate, and transmissioncharacteristics of the data.